Fuel Economy Calculator: MPG & L/100 km
Measure actual gas mileage from fill-ups. Combine multiple tanks, convert US or Imperial MPG and L/100 km, and estimate cost per mile or kilometer.
Your inputs
Example inputs are hypothetical. Choose units and assumptions that match your measurements.
Your result
Enter your values, then choose Calculate.
Calculations stay in this browser. Display rounding does not change the underlying calculation.
Calculation breakdown
Method, assumptions and worked example
Measure fuel consumption from full-tank intervals
Fill the tank and record the odometer. At the next full refill, record distance traveled and the amount needed to refill. The first fill establishes the baseline; it is not fuel consumed during that interval. If you make partial fills, add their fuel to the next complete interval rather than treating each as a full-tank reading.
Formulas and worked example
L/100 km = total liters ÷ total kilometers × 100. MPG = total miles ÷ total gallons. Driving 500 km on 40 L, then 300 km on 30 L, uses 70 L over 800 km: 8.75 L/100 km, 26.88 US MPG or 32.28 Imperial MPG. At 1.60 per liter, fuel costs 112 in your selected currency, or 0.14 per kilometer.
Why combined MPG is weighted
Average consumption must use total fuel and total distance. Simply averaging the MPG of a short tank and a long tank gives them the same influence and can distort your result. Enter up to 50 measured intervals here.
US versus Imperial gallons
A US gallon is 3.785411784 liters; an Imperial gallon is 4.54609 liters. One mile is 1.609344 kilometers. The same vehicle therefore has different numerical MPG in the two gallon systems. Lower L/100 km and higher MPG mean less fuel per distance.
Frequently asked questions
Should I use dashboard MPG or fuel receipts?
This tool is designed for measured distance and refill volume. Several comparable full-tank intervals reduce the effect of refill variation.
Does switching units convert my entries?
Yes. Existing distances, volumes and a supplied fuel price are converted together. Currency is only a label.
Can this predict trip costs?
It measures consumption from recorded fill-ups. Use the linked journey calculator to budget a future route with that consumption.
Method review and references
Formula and content reviewed on 10 October 2026. Worked examples are hypothetical. Methods and assumptions are explained on each page. Use actual measurements, product yields and applicable school or employment rules. These tools are independent estimates.
The calculation or selection method is described above. Use the relevant school policy, supplier quote or measurement definition when choosing inputs.