Materials, Labour and Production Overheads

Introduction

Production cost is not created by materials alone. It emerges from the coordinated use of material resources, human effort, equipment, energy, supervision, maintenance and production facilities. For a production manager, the central task is to measure these resources accurately, control avoidable losses and assign cost fairly to products, jobs, batches or processes. Reliable costing supports pricing, make-or-buy decisions, budgeting, operational control, productivity improvement and continuous improvement.

This chapter examines three major elements of manufacturing cost: materials, labour and production overheads. It distinguishes cost measurement from cost control. Measurement answers the question “What has been consumed and at what cost?” Control asks “Was the consumption necessary, efficient and aligned with standards?”

Learning Objectives

After studying this chapter, the learner should be able to:

• design controls for purchasing, receiving, storing and issuing materials;
• calculate inventory quantities and values using appropriate methods;
• distinguish normal and abnormal waste, scrap, spoilage and defective output;
• analyse labour time, overtime, idle time, incentives and productivity;
• classify, allocate, apportion and absorb factory overheads;
• select suitable overhead absorption bases and interpret under- or over-absorption;
• evaluate costing information for managerial decisions and operational improvement.

1. Materials Cost Management

1.1 Meaning and classification

Materials are physical inputs incorporated into a product or consumed in production. Direct materials can be economically traced to a specific product, job or batch. Timber in a table, steel in a fabricated frame and fabric in a garment are examples. Indirect materials support production but cannot be conveniently traced to individual output; examples include lubricants, cleaning supplies, welding electrodes and small tools.

Materials may also be classified by stage and purpose:

The classification should reflect the cost object and the information purpose. A component may be direct for one product but indirect for a high-volume product where individual tracing is uneconomic.

1.2 Procurement and receiving controls

An integrated materials system normally contains the following documents and controls:

1. Material requisition or bill of materials: specifies quantity, grade and technical requirements.
2. Purchase requisition: authorises the need and budget.
3. Request for quotation and supplier evaluation: compares price, quality, delivery, capacity and risk.
4. Purchase order: creates the contractual commitment.
5. Goods-received note: records quantity and condition received.
6. Inspection report: confirms conformity to specification.
7. Stores ledger or digital inventory record: records receipts, issues and balances.
8. Material issue note: authorises movement to a job, cost centre or department.

A three-way match among purchase order, goods-received note and supplier invoice reduces duplicate payment and unauthorised purchasing. Segregation of duties is important: the person ordering materials should not independently approve receipt and payment.

Supplier selection should consider total cost rather than invoice price alone. Total landed cost can include freight, insurance, duties, inspection, handling, financing and expected quality-related costs. Supplier scorecards may combine delivery reliability, rejection rate, responsiveness and cost performance.

1.3 Inventory quantity decisions

A basic economic order quantity (EOQ) model determines the order size that minimises ordering and holding costs under restrictive assumptions. The conventional formula is:

where Q* is the optimal order quantity in units per order, D is annual demand in units, S is ordering cost per order, and H is annual holding cost per unit. The model assumes relatively stable demand, constant ordering and holding costs, instantaneous replenishment, no shortages and a constant unit price. It is a benchmark, not a substitute for managerial judgement.

The reorder point indicates when an order should be placed:

where d is average demand per time period, L is lead time in the same time unit, and SS is safety stock. If demand and lead time are uncertain, safety stock should reflect the desired service level and the variability of demand during lead time. A simple periodic review system may instead order enough to cover demand until the next review plus lead time.

1.4 Inventory valuation and issue pricing

The principal issue-pricing methods are:

• FIFO: earliest receipts are issued first; ending inventory tends to reflect recent purchase prices.
• Weighted-average cost: the average cost of available units is applied to issues, usually after each receipt or over a period.
• Specific identification: the actual cost of identifiable items is assigned; it is appropriate for unique, high-value items.

Under rising prices, FIFO generally reports lower material consumption cost and higher closing inventory than an older-cost method, assuming physical flows and accounting flows are aligned. The choice should be consistent with the applicable financial reporting framework and internal costing policy.

1.5 Material losses, waste, scrap and spoilage

Waste is material with no recoverable value, such as evaporation or trimming dust. Scrap is residual material with some recoverable value. Spoilage refers to units that fail quality standards and cannot be economically brought to specification. Defectives can be corrected or reworked at additional cost.

Normal loss is expected under efficient operating conditions. Its cost is normally absorbed by good output. Abnormal loss arises from avoidable or unusual events, such as equipment failure, careless handling or defective input, and should be separately reported for corrective action rather than hidden in product cost. Recoverable scrap proceeds may reduce the cost of the related process or be credited to a factory overhead or scrap account according to policy.

For a process with input quantity I, normal loss rate r, and actual good output G, expected good output is:

where r is expressed as a decimal. If actual good output is below the expected quantity, the difference may indicate abnormal loss, subject to investigation and inspection of opening and closing work-in-process.

1.6 Material variances

Where standard costing is used, material performance may be divided into price and usage effects. With standard price SP, actual price AP, standard quantity allowed for actual output SQ, and actual quantity used AQ, the variances are:

A positive result is conventionally favourable when actual cost is below standard cost; a negative result is adverse. The price variance may be influenced by purchasing, while the usage variance may arise from production methods, material quality, design changes or waste. Responsibility should not be assigned mechanically: a low purchase price may cause poor quality and an adverse usage variance.

2. Labour Cost and Productivity

2.1 Direct and indirect labour

Direct labour is the cost of employees whose time can be traced economically to a product, job or process. Indirect labour supports production without being conveniently traceable, including supervisors, maintenance workers, material handlers and quality inspectors. Labour classification should follow causality and materiality, not job title alone.

A sound labour-cost system links employees, time and output. Common records include clock-in data, job cards, electronic time tickets, work orders, overtime authorisations and productivity reports. Time booked should reconcile with attendance time. Unexplained differences may indicate idle time, administrative delay, inaccurate recording or inappropriate standards.

2.2 Time analysis and idle time

Paid time may be divided into productive time, necessary non-productive time and avoidable idle time. Normal idle time may result from setting up machines, routine breaks, waiting for material or normal changeover. It is generally included in production overhead or absorbed through an appropriate rate. Abnormal idle time, caused by unusual breakdowns, strikes or prolonged material shortages, should be identified separately and investigated.

Overtime has two dimensions: the premium and the underlying hours. If overtime is required for a specific customer order or urgent job, the premium may be charged directly to that job. If overtime is caused by general capacity constraints or poor scheduling, it is usually treated as production overhead. Policies must comply with labour law, collective agreements and health-and-safety requirements.

2.3 Labour remuneration methods

Under time-rate payment, earnings are:

The method is simple and protects quality where output is difficult to measure, but it may provide limited motivation for higher productivity.

Under a piece-rate system:

It provides a direct output incentive, but it can encourage excessive speed, quality failures or unsafe behaviour if standards and controls are weak.

A bonus plan may pay time saved against a standard. Under the Halsey plan, for example:

The share is the worker’s agreed proportion of time saved. Under the Rowan plan:

These formulas assume that time allowed, actual time and hourly rate use consistent units. Incentive plans should be evaluated not only by labour cost per unit but also by quality, safety, machine utilisation, maintenance and employee well-being.

2.4 Labour productivity and variance analysis

A basic labour productivity measure is:

Units must be comparable across periods, and output should preferably be measured as good output rather than gross output. For mixed products, equivalent units, standard hours or value-added measures may be more meaningful.

With standard rate SR, actual rate AR, standard hours allowed SH and actual hours AH, standard labour variances are:

An efficiency variance may reflect skill, method, machine condition, material quality or standard-setting error. Managers should investigate causal chains rather than treating variance labels as proof of individual responsibility.

3. Production Overheads

3.1 Nature and classification

Production or factory overhead comprises indirect manufacturing costs. Examples include indirect materials, indirect labour, factory rent, depreciation, power, maintenance, production planning and quality-control costs.

Overheads can be classified by:

• Behaviour: fixed, variable or semi-variable;
• Function: production, administration, selling and distribution;
• Traceability: direct or indirect;
• Controllability: controllable or non-controllable relative to a manager and time horizon;
• Department: production departments and service departments.

Fixed cost remains constant in total within a relevant capacity range, whereas variable cost changes with an activity driver. Cost per unit behaves differently: fixed cost per unit declines as output rises, while variable cost per unit is approximately constant under stable conditions. Semi-variable cost contains both components and may require analysis using engineering studies, account analysis or high-low estimation.

3.2 Cost centres and responsibility centres

A cost centre is a location, person, machine group or department for which costs are accumulated. Production cost centres work directly on products; service cost centres support production, for example maintenance, stores, power generation and quality assurance. Establishing cost centres improves accountability and supports more defensible allocation.

Costs should be assigned according to the following hierarchy:

1. Allocation: charge the entire cost directly to a cost centre when it is identifiable.
2. Apportionment: distribute a shared cost among cost centres using a rational basis.
3. Reapportionment: transfer service-centre costs to production centres.
4. Absorption: charge production-centre overhead to units, jobs or processes.

Typical apportionment bases include floor area for rent, machine value for depreciation, number of employees for welfare, power consumption for electricity and purchase orders for procurement support. The basis should reflect resource consumption and be reviewed when technology or process design changes.

3.3 Service-department allocation

The direct method allocates service-department costs only to production departments and ignores services exchanged between service departments. The step-down method recognises some reciprocal service, depending on the sequence selected. The reciprocal method recognises mutual services fully, often through simultaneous equations. The more sophisticated method is more accurate but requires reliable data and may not be worthwhile when reciprocal services are immaterial.

3.4 Overhead absorption rates

An overhead absorption rate assigns production overhead to output. The general formula is:

The activity base may be direct labour hours, machine hours, direct labour cost, units produced or a combination of drivers. The numerator and denominator must relate to the same period and capacity assumption.

If a department budgets overhead of CU 480,000 and 24,000 machine hours, then:

A job using 150 machine hours absorbs CU 3,000. This rate is appropriate when machine time is the principal cause of overhead. A labour-intensive department may instead use a labour-hour rate.

A blanket rate applies one rate to an entire factory. A departmental rate uses separate rates for departments and is usually more accurate when departments have different technologies and cost structures. Activity-based costing (ABC) assigns overhead through activity pools and cost drivers, such as setups, inspections, material movements and purchase orders. ABC can improve product-cost accuracy where overhead is substantial and product diversity is high, although it increases data and maintenance requirements.

3.5 Under- and over-absorption

Actual overhead incurred may differ from overhead absorbed. Under-absorption occurs when absorbed overhead is less than actual overhead; over-absorption occurs when absorbed overhead exceeds actual overhead. Causes include volume changes, spending differences, inefficient use of resources, inaccurate budgets, abnormal events and incorrect activity forecasts.

A useful decomposition is:

The sign convention should be stated because some systems label a positive difference as adverse and others as under-absorption. Material variances should be investigated before being transferred to cost of sales, work-in-process, inventory or a variance account. Normal volume fluctuations may be included in product-cost analysis; abnormal events should remain visible to management.

4. Integrated Worked Example

A fabrication department budgets factory overhead of CU 360,000 and 18,000 machine hours. A job uses 120 machine hours, 900 kg of material at CU 8 per kg, and 75 direct labour hours at CU 18 per hour. Material waste of 2% is normal and has no recoverable value.

The machine-hour absorption rate is:

Material cost is:

Direct labour cost is:

Factory overhead absorbed is:

Therefore, the job cost before any selling or administrative cost is:

The normal waste is already included in the material cost. If the 2% loss is unexpectedly exceeded, the excess should be measured and investigated as abnormal loss rather than silently incorporated into the job.

5. Illustrative Case: Orion Components

Background

Orion Components manufactures two product families. Product A is produced in large batches on automated equipment; Product B is produced in small batches and requires frequent setups, inspections and material movements. The company has historically applied one factory-wide rate based on direct labour hours.

Problem

Although Product A appears profitable under the existing system, managers believe it consumes substantial machine capacity and energy. Product B appears less profitable, despite using fewer machine hours, because it receives a large share of overhead through labour hours. Customer quotations based on the existing cost information have produced inconsistent margins.

Analysis

A cross-functional team maps overhead activities and identifies three major cost pools:

The team validates driver data against maintenance, production and quality records. It finds that Product B consumes many setups and inspections, while Product A consumes machine hours and energy. The single labour-hour rate conceals these differences.

Approach and solution

Orion introduces departmental and activity-based rates for internal decision-making, while retaining statutory reporting requirements separately. Standards are reviewed quarterly. Quotation software displays material, labour, activity overhead and capacity-utilisation assumptions. The company also distinguishes normal setup time from abnormal waiting caused by missing components.

Outcome

The revised information leads to a price redesign for complex small batches, engineering changes that reduce setup frequency and a supplier-quality programme for defective inputs. Product A remains strategically important, but its capacity consumption is now visible. Product B is not abandoned; instead, its price and process design are corrected.

Learning points

1. A costing system is a model of resource consumption, not a perfect physical measurement.
2. A rate is only as useful as its cost driver and capacity assumption.
3. Variances require operational investigation; they are not automatically evidence of poor employee performance.
4. Cost accuracy and cost control are related but distinct: ABC may improve attribution, while lean methods may reduce consumption.
5. Cost information should not encourage unsafe work, excessive overtime or quality sacrifice.

6. Governance, Technology and Contemporary Practice

Materials and labour systems increasingly use enterprise resource planning, barcode scanning, RFID, machine data and electronic time capture. Automated data can improve timeliness, but master-data errors, inaccurate routings and unverified machine signals can produce highly precise but misleading costs. AI may assist demand forecasting, anomaly detection, supplier-risk scoring and predictive maintenance. Its outputs require human oversight, traceable data and controls against biased or unexplained decisions.

Cost records should comply with applicable accounting standards, tax rules, labour legislation, environmental obligations, collective agreements and internal delegation policies. Scrap disposal and hazardous-material handling may create environmental and legal responsibilities. Labour productivity systems must respect privacy, due process, lawful monitoring and occupational health. Incentives should never reward unsafe shortcuts or concealment of defects.

Best practice is to combine financial and operational indicators: material yield, inventory accuracy, supplier rejection, labour productivity, first-pass yield, overtime, idle time, machine utilisation, energy per unit, overhead absorption and customer profitability. A balanced review prevents managers from reducing one cost while increasing total cost elsewhere.

Chapter Summary

Materials, labour and production overheads are the principal building blocks of manufacturing cost. Materials require disciplined procurement, receiving, storage, issue, valuation and loss reporting. Normal loss is expected and absorbed by good production, whereas abnormal loss should be separately investigated. Inventory decisions balance ordering, holding, service and operational risk.

Labour costing depends on accurate time records, a clear distinction between direct and indirect labour, appropriate treatment of idle time and overtime, and incentive systems that integrate cost, quality and safety. Productivity and standard variances are diagnostic tools rather than automatic judgements of responsibility.

Production overheads must be classified, accumulated in cost centres, allocated or apportioned using causal bases, reapportioned from service departments and absorbed into output using defensible rates. Departmental rates and activity-based costing can improve accuracy where processes and products differ substantially. Under- and over-absorption reveal differences between actual cost and assigned cost and should trigger investigation. Effective production-cost management combines accounting discipline with engineering knowledge, operational data, ethical governance and continuous improvement.

Key Terms

Material allocation: Direct charging of an identifiable material cost to a cost object.

Material requisition: Authorised document requesting materials for production.

FIFO: Inventory issue method assuming earliest receipts are issued first.

EOQ: Order quantity that balances ordering and holding costs under stated assumptions.

Reorder point: Inventory level at which replenishment should be initiated.

Safety stock: Buffer inventory held against uncertainty.

Normal loss: Expected loss under efficient operating conditions.

Abnormal loss: Unusual or avoidable loss requiring separate investigation.

Scrap: Residual material with recoverable value.

Direct labour: Labour economically traceable to a product, job or process.

Idle time: Paid time during which productive work is not performed.

Labour productivity: Output achieved per unit of labour input.

Cost centre: Organisational or operational unit for accumulating costs.

Allocation: Direct assignment of a cost to a cost centre or object.

Apportionment: Distribution of a shared cost using a rational basis.

Overhead absorption rate: Rate used to charge production overhead to output.

Under-absorption: Absorbed overhead lower than actual overhead.

Activity-based costing: Costing system using activities and their drivers to assign overhead.

Standard quantity allowed: Quantity that should be used for actual output under standard conditions.

Variance: Difference between an actual, standard or budgeted amount and its comparator.

Review Questions

Short Answer Questions

1. Distinguish direct materials from indirect materials and provide one example of each.
2. What is the purpose of a goods-received note and inspection report?
3. Explain the difference between normal and abnormal loss.
4. Why is idle time separately analysed in labour costing?
5. Define overhead absorption rate and state one possible activity base.

Long Answer Questions

1. Explain the complete materials control cycle from purchasing through issue and inventory valuation.
2. Discuss time-rate, piece-rate, Halsey and Rowan remuneration methods, including their behavioural risks.
3. Explain allocation, apportionment, service-department reapportionment and absorption of factory overhead.
4. Compare blanket, departmental and activity-based overhead rates and identify circumstances favouring each.
5. Discuss how production managers should use material, labour and overhead variances without creating dysfunctional behaviour.

Analytical / Application Questions

1. A department budgets CU 600,000 overhead and 30,000 machine hours. A job uses 220 machine hours, 1,000 kg of material at CU 6 per kg and 80 labour hours at CU 20 per hour. Calculate the overhead absorption rate and total prime-plus-absorbed-overhead cost.
2. A process receives 5,000 units and has a normal loss rate of 4%. Actual good output is 4,700 units. Calculate expected good output and identify the quantity requiring investigation.
3. A firm uses labour hours to absorb overhead although one product requires many setups and inspections while another requires mostly machine time. Evaluate the weakness of the current system and recommend a revised costing approach.

Multiple Choice Questions with Answers

Question 1

Which document normally confirms the quantity and condition of materials received?

A. Purchase requisition

B. Goods-received note

C. Material issue note

D. Labour time ticket

Correct Answer: B. Goods-received note

Question 2

Annual demand is 10,000 units, ordering cost is CU 50 per order, and annual holding cost is CU 2 per unit. Using Q* = √(2DS/H), what is the EOQ?

A. 500 units

B. 707 units

C. 1,000 units

D. 2,000 units

Correct Answer: C. 1,000 units

Question 3

Which loss is generally expected under efficient operating conditions?

A. Abnormal loss

B. Normal loss

C. Fraudulent loss

D. Exceptional loss

Correct Answer: B. Normal loss

Question 4

A worker is paid CU 18 per hour and works 40 hours. Under a time-rate system, earnings are:

A. CU 360

B. CU 540

C. CU 720

D. CU 900

Correct Answer: C. CU 720

Question 5

Which item is usually classified as indirect labour?

A. Welder working on an identified customer job

B. Assembler producing a traceable component

C. Factory supervisor overseeing several jobs

D. Operator paid per unit of one product

Correct Answer: C. Factory supervisor overseeing several jobs

Question 6

Budgeted factory overhead is CU 480,000 and budgeted machine hours are 24,000. The absorption rate is:

A. CU 10 per machine hour

B. CU 20 per machine hour

C. CU 24 per machine hour

D. CU 48 per machine hour

Correct Answer: B. CU 20 per machine hour

Question 7

What is the correct sequence in overhead cost treatment?

A. Absorption, allocation, apportionment, reapportionment

B. Allocation, apportionment, reapportionment, absorption

C. Apportionment, absorption, allocation, reapportionment

D. Reapportionment, allocation, absorption, apportionment

Correct Answer: B. Allocation, apportionment, reapportionment, absorption

Question 8

Which overhead method is most suitable when products consume very different numbers of setups, inspections and material movements?

A. Single blanket rate based on units

B. Activity-based costing

C. No-overhead method

D. Specific identification of direct labour only

Correct Answer: B. Activity-based costing

Question 9

If actual overhead exceeds absorbed overhead, the result is:

A. Over-absorption

B. Under-absorption

C. Zero absorption

D. Material price variance

Correct Answer: B. Under-absorption

Question 10

Using Labour\ efficiency\ variance = SR(SH − AH), if the standard rate is CU 25, standard hours are 1,000 and actual hours are 1,100, the variance is:

A. CU 2,500 favourable

B. CU 2,500 adverse

C. CU 27,500 favourable

D. CU 27,500 adverse

Correct Answer: B. CU 2,500 adverse