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Fundamentals of Financial and Cost Accounting · Cost, Cost Centre, Cost Unit and Cost Drivers

Cost Unit and Units of Measurement Explained

Updated 10 October 2026 · Fact-checked

A cost unit is a unit of product, service or time in terms of which cost is measured and expressed. Examples are a tonne of steel, a kWh of electricity or a bed-day in a hospital. Composite units combine two measures, such as tonne-km or passenger-km. In MCQs, match the industry to its usual unit.

Understand Cost Unit and Units of Measurement

Cost is only useful when you can say how much it is per something. A cost unit is that "something". It is the unit of product, service or time for which you measure and state cost.

A steel mill may say cost is ₹40,000 per tonne. A hospital may say cost is ₹2,500 per bed-day. A school may say cost per student. In each case the cost unit gives you a base to compare, control and price.

Cost units are of two kinds. A simple (single) unit uses one measure, such as a tonne, a litre, a metre or a piece. A composite (compound) unit joins two measures, such as tonne-km, passenger-km or patient-day. Composite units are used where service depends on both quantity and distance or time.

Do not confuse a cost unit with a cost centre. A cost centre is a location, person or item for which costs are collected. A cost unit is what you measure the cost of. Cost centre answers "where was cost incurred?". Cost unit answers "cost of what?".

A good cost unit is easy to understand, measurable, suited to the industry, and stable enough to compare across periods.

Key formulas to remember

Cost per unit
Cost per unit = Total cost ÷ Number of cost units
Use the same cost unit for the cost and the output. Example: ₹60,000 ÷ 300 tonnes = ₹200 per tonne.
Composite unit: tonne-km (absolute)
Absolute tonne-km = Total tonnes carried × Distance in km (for each trip, then add)
Used in goods transport. Add trip by trip when loads or distances differ.
Composite unit: tonne-km (commercial)
Commercial tonne-km = Average load × Total distance travelled
Average load = (sum of loads at each stage) ÷ number of stages. Total distance is the full distance travelled, including the empty leg. Illustration: a truck carries 10 tonnes over 200 km and returns empty over 200 km. Average load = (10 + 0) ÷ 2 = 5 tonnes. Total distance = 400 km. Commercial tonne-km = 5 × 400 = 2,000. This simple average gives the same result as the absolute figure only when the legs are of equal length, as here. If the legs differ in distance, weight the average load by distance, or use the stage method given in the question.
Composite unit: passenger-km
Passenger-km = Number of passengers × Distance in km
Used for buses, trains, airlines.

How to solve Cost Unit and Units of Measurement questions

Use this method for any question on cost units, whether it asks for the unit of an industry or a calculation with a composite unit.

  1. 1Identify the industry or activity: manufacturing, transport, power, hospital, education, hotel and so on.
  2. 2Ask what the business sells or delivers: a physical product, a service, or time of service.
  3. 3Choose the unit that measures that output directly, for example tonne, kWh, bed-day, passenger-km.
  4. 4If the service depends on two factors such as load and distance, use a composite unit.
  5. 5For a calculation, compute the number of units first, such as passengers × km or tonnes × km.
  6. 6Divide total cost by the number of units to get cost per unit.
  7. 7Check units in your answer: the result must be in rupees per the chosen unit.
  8. 8Scan the four options and eliminate any unit that does not fit the industry.

Quickest way: Industry-to-unit matching

When to use it: Use for definition-type MCQs that ask for the cost unit of an industry or service.

  1. Read the industry word first.
  2. Recall the standard pairing: steel, cement, sugar - tonne; electricity - kWh; brick - 1,000 bricks; hospital - patient-day or bed-day; transport - passenger-km or tonne-km; hotel - room-day; school - student; cinema - ticket or seat; textile - metre.
  3. If the option has two measures joined, it is a composite unit and fits transport or similar services.
  4. Eliminate options that measure input (such as labour hours) when the question asks for output unit.
  5. Pick the best fit and move on.

Common mistakes in Cost Unit and Units of Measurement

  • Ignoring that the empty return leg contributes zero to absolute tonne-km, or averaging load across legs for absolute tonne-km.

    Students try to use total distance or an average load instead of working leg by leg.

    Fix: Multiply the actual load by the distance for each leg and add. An empty leg gives 0 × distance = 0.

  • Treating cost unit and cost centre as the same thing.

    Both words begin with "cost" and appear in the same chapter.

    Fix: Cost centre is where cost is collected. Cost unit is what the cost is measured for.

  • Calling passenger-km a simple unit.

    Students see one word and miss the two measures.

    Fix: If two measures are multiplied, such as passengers and km, it is composite.

  • Adding passengers and km instead of multiplying them.

    The hyphen in the name looks like a plus or minus.

    Fix: Multiply the two measures. 40 passengers over 25 km is 1,000 passenger-km.

  • Choosing an input measure like machine hours as the cost unit of a product.

    Machine hours are common in other topics.

    Fix: Cost unit is an output measure. Machine hours is a basis for absorbing overheads.

  • Using the same unit for all industries, such as "per piece" everywhere.

    Piece feels like the safest answer.

    Fix: Match the unit to the industry, for example kWh for power and bed-day for a hospital.

Worked examples

Example 1

A truck carries 10 tonnes from Pune to Nashik, a distance of 200 km, and returns empty. The total cost of the round trip is ₹24,000. Find the cost per absolute tonne-km.

Show the solution
  1. Absolute tonne-km counts only loaded weight times distance.
  2. Outward trip: 10 × 200 = 2,000 tonne-km.
  3. Return trip: 0 × 200 = 0 tonne-km.
  4. Total absolute tonne-km = 2,000.
  5. Cost per tonne-km = ₹24,000 ÷ 2,000 = ₹12.

Answer: ₹12 per absolute tonne-km

Example 2

Using the same trip (10 tonnes over 200 km, empty return of 200 km, total cost ₹24,000), find the cost per commercial tonne-km.

Show the solution
  1. Commercial tonne-km = Average load × Total distance travelled.
  2. Average load = (sum of loads at each stage) ÷ number of stages.
  3. Loads on the two legs are 10 tonnes and 0 tonnes.
  4. Average load = (10 + 0) ÷ 2 = 5 tonnes. The simple average is fine here because both legs are 200 km.
  5. Total distance travelled = 200 + 200 = 400 km.
  6. Commercial tonne-km = 5 × 400 = 2,000.
  7. Cost per commercial tonne-km = ₹24,000 ÷ 2,000 = ₹12.

Answer: ₹12 per commercial tonne-km (equal to the absolute figure here only because both legs are 200 km)

Example 3

Which of the following is a composite cost unit? (A) Tonne of cement (B) Kilowatt-hour (C) Passenger-km (D) Metre of cloth

Show the solution
  1. A composite unit joins two measures.
  2. Tonne and metre are each a single measure of output. Kilowatt-hour is conventionally treated as a single unit of energy in costing, even though it is built from kilowatt and hour.
  3. Passenger-km is the standard composite (compound) unit. It combines the number of passengers and the distance.
  4. So option C is the composite unit.

Answer: (C) Passenger-km

Exam tips

  • Memorise the industry-unit pairs. Most MCQs are direct matches.
  • If an option has a hyphen between two measures, check whether it fits transport or a similar service.
  • For tonne-km questions, write the trips in a small list and multiply each. Do not mix loaded and empty legs.
  • Read whether the question asks for absolute or commercial tonne-km before calculating.
  • Do not leave any question blank. There is no negative marking, so guess after eliminating options.

Practice questions from Cost, Cost Centre, Cost Unit and Cost Drivers

Cost Unit and Units of Measurement in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Cost Unit and Units of Measurement: frequently asked questions

What is a cost unit in simple words?

It is the unit in which you measure and state cost, such as a tonne, a litre or a bed-day. It lets you say cost per unit of output or service.

What are composite cost units with examples?

A composite unit combines two measures. Common examples are tonne-km for goods transport and passenger-km for bus, rail or air services.

How is a cost unit different from a cost centre?

A cost centre is a place, person or item where costs are collected. A cost unit is the unit of product or service whose cost you measure.

How do I select a cost unit for a business?

Pick a unit that is easy to measure, directly linked to what the business delivers, and consistent over time. It should also suit the industry and help in control and pricing.