# Absolute Tonne-Km vs Commercial Tonne-Km

When a goods truck carries different loads on different stretches of a journey, tonne-km can be calculated in two ways.

## 1. Absolute Tonne-Km Method

Calculate tonne-km for each leg separately and add them up. This is the 'normal' / accurate method.

$$\text{Absolute Tonne-Km} = \Sigma (\text{Tonnes in segment} \times \text{Distance of segment})$$

## 2. Commercial Tonne-Km Method

Take the average load carried during the entire journey and multiply by total distance.

$$\text{Commercial Tonne-Km} = \text{Average tonnes} \times \text{Total Distance}$$

where:

$$\text{Average tonnes} = \frac{\text{Sum of loads on each leg}}{\text{No. of legs}}$$

## Comparison Summary

Aspect	Absolute Tonne-Km	Commercial Tonne-Km
Approach	Segment-wise multiplication	Average × Total distance
Accuracy	More accurate	Less accurate (approximation)
When used	When precise costing needed	Quick estimation

Worked example

### Example 1

Example:

A truck makes a journey with the following loads on three legs:

Total distance = 8,250 km (3 legs together).

Absolute Tonne-Km: (Distance of leg 1 × 4) + (Distance of leg 2 × 3) + (Distance of leg 3 × 2) — calculated leg by leg.

Commercial Tonne-Km:

$$\frac{4 + 3 + 2}{3} \text{ tonnes} \times 8250 \text{ km} = 3 \times 8250 = 24{,}750 \text{ tonne-km}$$

⚠️ Common exam mistakes

Confusing the two methods — always read the question carefully to see which is asked
Using simple average when weights/distances are unequal — commercial tonne-km uses arithmetic mean of loads regardless of segment length
Forgetting that absolute tonne-km is the more accurate of the two

Reference:

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