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Fuel Economy Calculator

Enter distance driven, fuel used, and optional price per litre. You get metric consumption (L/100km), the same figure as US miles per gallon, and trip fuel cost.

Calculate

Measurements convert when you switch units

km
L
€

Updates as you type

Result

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The formula

L/100km is litres used per 100 km. US MPG is the same efficiency as miles per US gallon (235.215 ÷ L/100km). Trip cost is litres × price.

L/100km = (Litres ÷ km) × 100 · US MPG ≈ 235.215 ÷ (L/100km) · Cost = Litres × Price

Worked example

  1. 100 km on 7 L at €1.60/L
  2. L/100km = (7 ÷ 100) × 100 = 7.00 (litres per 100 km)
  3. US MPG ≈ 235.215 ÷ 7 ≈ 33.6 miles per US gallon · Cost = 7 × 1.60 = €11.20

Result: 7.00 L/100km · ≈ 33.6 US MPG · €11.20

How fuel economy is calculated

We measure how much fuel your trip used per distance (L/100km), convert that to U.S. miles per gallon for comparison, and optionally multiply litres by price for trip cost. Inputs are kilometres and litres.

L/100 km

This is litres of fuel used for every 100 km driven. Lower L/100km means better efficiency. City stop-and-go, cold starts, roof boxes, and underinflated tires raise the figure versus steady highway cruising.

US MPG

Miles per US gallon — how many miles the car travels on one U.S. gallon (≈ 3.785 L). We convert with the factor 235.215 ÷ (L/100km). UK imperial gallons are larger (4.546 L), so UK MPG figures are higher for the same car — this page reports U.S. MPG only.

Trip cost

Cost = litres × price per litre in the page currency. It does not average multiple fill-ups or account for idle time separately.

What we do not model

No WLTP/EPA label lookup, hybrid EV modes, or elevation correction. Official lab ratings differ from real-world fill-up math.

Interesting facts

WLTP in Europe

Since 2018, EU car labels use WLTP test figures — generally more realistic than the older NEDC standard.

MPG vs L/100 km

Miles per gallon rises as efficiency improves; liters per 100 km falls. They move in opposite directions for the same car.

City vs highway

Stop-and-go traffic, cold starts, and short trips raise consumption versus steady highway cruising.

Tire pressure and load

Underinflated tires and heavy cargo quietly increase fuel use — maintenance is free economy.

Hybrids and short trips

Hybrids shine in urban stop-go. On long cold highway runs, their advantage can shrink.

Frequently asked questions

Divide litres used by kilometres driven, then multiply by 100. Example: 7 L over 100 km → 7.0 L/100km.

This page converts to U.S. MPG (U.S. gallon ≈ 3.785 L). UK imperial gallons are larger, so UK MPG numbers are higher for the same consumption.

One measures distance per volume; the other measures volume per distance. Better efficiency raises MPG and lowers L/100km.

Inputs are kilometres and litres. Convert miles → km and gallons → litres first (or use a unit converter), then calculate.

Lab cycles (WLTP, EPA) are standardized comparisons. Your fill-up average reflects weather, traffic, load, and driving style.

References

  1. Fuel economy tools — U.S. Department of Energy — FuelEconomy.gov Official U.S. fuel-economy ratings and consumer guidance.
  2. WLTP explanation — European Commission Background on the EU WLTP test procedure for vehicle labels.
  3. NIST — SI units — National Institute of Standards and Technology Authoritative SI length and volume context for metric inputs.