Fuel Economy Calculator

Convert fuel economy

Trip fuel cost

The trip cost uses the fuel economy entered in the converter above.

How it works

MPG measures distance per unit of fuel; L/100 km measures fuel per unit of distance — they are reciprocals, linked by one constant: L/100 km = 235.215 ÷ MPG (the constant folds in 100 km = 62.137 miles and 1 US gallon = 3.78541 liters). km/L is the plain reciprocal of L/100 km scaled: km/L = 100 ÷ L/100 km. Because L/100 km runs backwards (lower is better), doubling MPG does not halve the number the same way — 20 MPG is 11.76 L/100 km and 40 MPG is 5.88.

Trip cost: fuel used = distance ÷ economy, worked in consistent units, and cost = fuel used × price per unit. This page uses US gallons throughout; a UK (imperial) gallon is about 20% larger, so UK MPG figures convert differently — convert an imperial MPG to US first by multiplying by 0.8327.

Worked example: 30 MPG = 235.215 ÷ 30 = 7.84 L/100 km = 12.75 km/L. A 300-mile trip at 30 MPG burns exactly 10 gallons; at $3.50 per gallon that is $35.00.

Frequently asked questions

Is 7 L/100 km good? 7 L/100 km ≈ 33.6 MPG — solid for a gasoline car. Around 5–6 L/100 km (39–47 MPG) is hybrid territory; 10+ L/100 km (under 23.5 MPG) is truck and large-SUV territory.

Why do the same car's US and European ratings look unrelated? They are the same fuel use in reciprocal units, often on different official test cycles as well — so a European figure converted exactly still may not match the US window-sticker number. Convert the units here; treat test-cycle differences as a separate gap.

How do I get my real MPG? Fill the tank, reset the trip odometer, drive, then fill again and divide miles driven by gallons used. That measured figure — not the dashboard estimate — is the best input for the trip cost above.