How the Mileage Calculator works.
US customary: MPG = miles ÷ US gallons; metric: L/100 km = litres ÷ kilometres × 100Enter values in the units named in each field. The calculator retains precision during the calculation and rounds displayed currency and measurements for readability.
Worked example for the Mileage Calculator.
For this Mileage Calculator example, with Measurement system: US customary (miles + US gallons); Trip distance (miles or km): 120; Fuel used (US gallons or litres): 4, the calculator returns 30.00 MPG. US-customary fuel economy from your entered miles and US gallons.
Measure one complete refill interval
For the most useful fuel-economy check, start after a full fill, record the odometer or reset the trip meter, drive normally, then refill to a comparable level. Use the distance driven and the fuel added at that second fill. A partial fill, a different pump shut-off point, or mixing fuel from different intervals can distort a single-trip result.
Keep the distance and fuel units together
In US customary mode, FigureNest divides miles by US gallons to report miles per gallon (MPG). In metric mode, it calculates litres used per 100 kilometres (L/100 km). Do not enter imperial gallons as US gallons, and do not combine kilometres with gallons or miles with litres. Convert first or select the matching mode.
How to interpret the result
Higher MPG means more distance from each US gallon, while lower L/100 km means less fuel used to travel 100 km. Compare several similar refill-to-refill intervals rather than treating one tank as a permanent vehicle rating. Traffic, idling, towing, speed, temperature, tyre pressure, route profile and short trips can all move the result.
Common mileage-check mistakes
The largest practical errors usually come from a partial refill, recording the wrong distance, entering the dashboard estimate instead of fuel actually added, choosing the wrong unit system, or comparing unlike trips. Keep the receipt and odometer reading until you have checked the calculation, and avoid rounding the distance or fuel amount before the final result.
Use several tanks for a trend
A single interval is useful for a quick check, but several full-tank intervals provide a better picture of typical fuel economy. If one result changes sharply, check the source readings and driving conditions before assuming the vehicle has developed a fault. This calculator measures observed consumption; it does not diagnose mechanical problems or predict fuel prices.
What this calculator does not include.
This result describes the refill interval you entered. It does not correct odometer error, verify pump calibration, distinguish idling from moving fuel use, convert imperial gallons to US gallons, reproduce an official laboratory fuel-economy test, diagnose a vehicle, or predict future consumption. Refill level, towing, load, traffic, weather, tyre pressure, speed and route can materially change real-world fuel use.
Reference guidance and methodology.
Mileage Calculator questions.
What does the Mileage Calculator measure?
It measures fuel economy from distance travelled and fuel actually used over the same interval. US customary mode reports MPG; metric mode reports L/100 km.
Why should I calculate from a full refill?
Using comparable full refills makes the fuel added a better estimate of what was consumed since the previous fill. Partial fills and different pump shut-off points can make a single interval misleading.
Is higher always better?
For MPG, a higher number means better fuel economy. For L/100 km, a lower number means better fuel economy because fewer litres are used per 100 km.
Can I compare MPG directly with L/100 km?
Not numerically. They use inverse conventions and different units. Compare results within the same unit system or convert them before comparing.
Why can my result differ from the dashboard?
A dashboard estimate may use vehicle sensor data and its own averaging window. This calculator uses only the distance and refill fuel you enter, so different intervals, rounding, idling and refill variation can produce a different value.