How to calculate fuel consumption: the full-tank method

Your trip computer says 7.2 L/100 km, but the tank somehow empties like it's 9? Factory readings are typically 10–20% low: the ECU estimates them from injection time — ignoring warm-ups, traffic and short trips. Real consumption is measured simply: at the pump and on the odometer.

The full-tank method, step by step

1. Fill up until the pump nozzle clicks off and reset the trip odometer (or note the mileage).
2. Drive as usual until a good chunk of the tank is gone — the more, the more accurate (300+ km).
3. Fill to click-off again, at the same pump, and note the liters and the distance driven.
4. Consumption = liters ÷ kilometers × 100.

Example: between two full fill-ups you drove 460 km and poured in 36 liters. Consumption = 36 ÷ 460 × 100 = 7.8 L/100 km.

Why "until click-off" and at the same pump? Nozzles cut off at different sensitivities, and pumps flow at different rates. The more consistent your second fill-up, the more accurate the number.

Why this beats the trip computer

You're measuring fuel actually delivered — the very liters you paid for. The computer estimates flow from injector open-time, and its readings drift with injector wear, rail pressure, even firmware version. A 1–1.5 L/100 km gap is completely normal.

What moves consumption the most

• Warm-ups and short trips — in winter, consumption can jump by a third.
• Traffic — stop-and-go is the most expensive driving there is.
• Speed — past 110–120 km/h, aerodynamics eats everything the engine gains.
• Tire pressure — 0.5 bar low adds 3–5%.
• Driving style — smooth vs. full throttle is up to a 20% difference.

That's why a single measurement says little: consumption is a trend. If it used to be 7.8 and now reads 9.2 on the same routes — the car is asking for diagnosis: sensors, air filter, lambda probe, or out-of-season tires.

How PitStop does it for you

The app does exactly what's described above — automatically. Every fill-up with mileage lands in the journal; PitStop builds average consumption, monthly dynamics and cost per kilometer. Spot an outlier on the chart — open the entry and see it was that trip to the countryside with a full trunk.

For accuracy, partial fill-ups (not to full) don't pollute the stats — they're averaged into the next full one.

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