How to Measure Fuel Consumption Across a Fleet

How do you measure fuel consumption across a fleet?

Fleet fuel consumption is measured per vehicle as litres consumed per 100 kilometres travelled (or kilometres per litre, depending on preference), calculated over a consistent period, and compared against that vehicle’s own baseline and against similar vehicles doing similar work.

Why per-vehicle measurement matters more than a fleet total

A single fleet-wide fuel spend figure is affected by fuel price, total distance travelled, and the mix of vehicles in the fleet — none of which tell you whether any individual vehicle is running efficiently. Two fleets could have identical total fuel spend for very different reasons: one running efficiently at high volume, the other running inefficiently at lower volume. Per-vehicle consumption is what actually separates those two situations.

The basic calculation

For any given period:

Litres consumed ÷ (kilometres travelled ÷ 100) = litres per 100km

For example, a vehicle that used 180 litres over 1,500 km:

180 ÷ (1,500 ÷ 100) = 180 ÷ 15 = 12 litres per 100km

That figure only becomes useful once you have something to compare it against — the vehicle’s own historical average, the manufacturer’s expected consumption, or similar vehicles elsewhere in the fleet.

What to compare it against

1. The vehicle’s own baseline. Most vehicles have a fairly consistent consumption rate under similar conditions. A sustained increase from that baseline — not a single high reading — is what’s worth investigating.
2. Manufacturer expected consumption, acknowledging that real-world figures are usually higher than the manufacturer’s rated figure, particularly for loaded commercial vehicles in stop-start conditions.
3. Similar vehicles in the fleet. If five identical bakkies are averaging 11–12 litres per 100km and one is consistently at 15, that’s a genuine outlier worth investigating — a mechanical issue, a driving behaviour pattern, tyre pressure, or a load difference.

What causes a consumption exception

Once a vehicle is flagged as a genuine outlier, the usual causes are:

• Driver behaviour — harsh acceleration and speeding increase consumption directly.
• Excessive idling — consuming fuel without covering distance (see how excessive idling affects your fleet).
• Mechanical issues — a poorly tuned engine, low tyre pressure, or a dragging brake can all increase consumption without an obvious symptom.
• Load and route differences — sometimes the vehicle isn’t the problem; it’s simply doing harder work than the vehicles it’s being compared against.

Where fuel card data fits in

Fuel card transaction data adds a second layer: cross-checking litres purchased against a vehicle’s actual distance and location can flag fills that don’t match the vehicle’s travel pattern at all — a more direct way to catch misuse than consumption analysis alone.

This combined view — consumption per vehicle plus fuel card cross-checking — is the basis of ongoing fuel management as part of SALT’s fleet management service.