THE NUMORIX GUIDE
How to use the Fuel Economy Converter
Last reviewed September 14, 2026
What this calculator does
The engine uses liters per 100 kilometers as its intermediate unit.
Formula and method
The engine uses liters per 100 kilometers as its intermediate unit. It applies L/100 km = 235.215 / US mpg, 282.481 / UK mpg, L/100 km = 100 / km/L, and the identity for an input already in L/100 km, then computes each requested output by the reciprocal formula.
Variables and inputs
Enter a positive fuel-economy value and choose MPG (US), MPG (UK), L/100km, or km/L. The UI rejects nonpositive values on conversion and returns all four results rounded to four decimal places. US and UK mpg use different gallon sizes.
Worked example
For 30 MPG (US), the intermediate value is 235.215 / 30 = 7.8405 L/100 km. The reciprocal output is 100 / 7.8405 = about 12.7543 km/L, while 30 US mpg is not 30 UK mpg because the gallon definitions differ.
How to interpret the result
MPG and km/L increase as a vehicle travels farther on a unit of fuel, while L/100 km decreases as efficiency improves. The figures describe fuel consumed over distance, not engine power, range, or a guaranteed trip result.
Common mistakes to avoid
Always identify US versus UK mpg before comparing values. Do not multiply mpg by 235.215 when converting to L/100 km; the relationship is reciprocal. Keep the distance and volume convention consistent and do not confuse fuel economy with fuel consumption for a fixed tank range.
Assumptions and limitations
The constants are rounded and the calculator does not account for driving speed, traffic, temperature, terrain, payload, tire pressure, fuel blend, or test-cycle differences. A zero or negative value is not meaningful even though the underlying engine would produce a division result if called directly. Real-world economy is an average measurement, not a constant.