Mileage Calculator
Calculate vehicle fuel consumption
🔒 Runs locally · Method · · Disclaimer · Mileage Calculator
Mileage Calculator helps you calculate vehicle fuel consumption without a spreadsheet. Fill in Distance (km) and Fuel Used (L) on Mileage and read your answer immediately. Nothing in Mileage is a black box. Use Mileage for a reliable number, fast. You can disconnect once Mileage has loaded; the arithmetic runs locally. Looking for free mileage calculator or free online mileage calculator? Mileage covers both. The labels in Mileage match the terms in its result. Start with Mileage; the first number takes seconds.
What 400 km on 30 litres is
That is 13.3 km per litre, or 7.5 L/100 km, or about 31.4 miles per gallon on the US gallon.
The figure is a tank-to-tank average, not a trip measurement: filling to the same point both times is what makes the litres column an honest measure of fuel burned.
The formula and the three units
Consumption (km/L) = distance ÷ fuel used. 400 ÷ 30 = 13.3 km/L.
Two other conventions matter because they run in opposite directions. L/100 km is 100 ÷ 13.3 = 7.5 — lower is better. MPG (US) is km/L × 2.352, giving 31.4 — higher is better. Comparing a km/L figure with an L/100 km figure without converting is the most common way to misread economy by a factor of ten.
Worked example
Distance 400 km, fuel 30 L → 13.33 km/L.
L/100 km = 100 / 13.33 = 7.5.
MPG US = 13.33 × 2.352 = 31.4.
MPG imperial = 13.33 × 2.825 = 37.7 (the imperial gallon is 4.546 L against 3.785).
Getting a fuel figure you can trust
Fill the tank until the pump clicks off, reset the trip meter, drive normally, then fill again at the same pump and record the litres. The second fill is the fuel actually burned over the distance shown. One tank is noisy — a 5% error in the litres reading moves a 31 mpg result by about 1.5 mpg — so average three tanks before drawing conclusions.
What changes the number
- Speed. Aerodynamic drag rises with the square of speed; 120 km/h can cost 20–25% more fuel than 90 km/h.
- Tyre pressure. Under-inflation adds rolling resistance and typically 1–3%.
- Cold starts and short trips. An engine running rich while warming up can double consumption on a 3 km commute.
- Load and roof bars. A roof box is worth roughly 10–20% at highway speed.
What the number is not
It is not the official homologated figure. WLTP or EPA test cycles run in controlled conditions without traffic, and real-world results are routinely 10–25% worse. Treat a personal average as the number to plan with.
Frequently Asked Questions
Is 13.3 km/L good?
It is about 31 mpg US, which is typical for a mid-size petrol car or a small SUV. Modern hybrids reach 20–25 km/L; older large petrol engines often sit at 8–10 km/L.
How do I convert km/L to L/100 km?
Divide 100 by the km/L figure. 13.3 km/L is 100 ÷ 13.3 = 7.5 L/100 km. The two scales are inverses, so an improvement on one is a decrease on the other.
Why do US and imperial mpg differ?
Different gallon sizes. A US gallon is 3.785 litres and an imperial gallon is 4.546, so the same car returns about 20% higher mpg in imperial units — 31.4 US becomes 37.7 imperial.
Can I use this for a partial tank?
Yes, as long as you started from a full tank and refill to the same level. Starting from a half tank makes the litres figure unrelated to the distance travelled.
Why is my trip computer different?
It estimates from injector pulse width rather than measuring fuel, and often ignores idling and cold-start enrichment. Tank-to-tank arithmetic is the reference it is being compared against.
Browse the Auto & Transport hub
Trip Time Calculator and other Auto & Transport tools
Trip Time Calculator · Stopping Distance · Car Carbon Footprint · E-Bike Range Calculator · Quarter-Mile ET Calculator · EV Charging Cost · Auto & Transport Guides