Fuel Economy Converter

Identify economy or consumption

MPG and km/L describe distance per fuel: a larger value covers more distance for the same fuel amount. L/100km describes consumption: a smaller value uses less fuel for the same distance. Choose the quantity before interpreting the direction of a change.

Name the gallon convention

A US liquid gallon is 3.785411784 L; an Imperial gallon is 4.54609 L. The same consumption therefore produces different MPG numbers. A hypothetical 30 US MPG is approximately 36.02849777 Imperial MPG. The source’s convention matters more than the place where you read it.

• Unit systems and named conventions
• Volume units
• Imperial MPG to US MPG

Use the reciprocal calculation

For MPG, L/100km = (100 × liters per gallon / kilometers per mile) / MPG. An international mile is 1.609344 km, giving a US numerator of approximately 235.2145833333 and an Imperial numerator of approximately 282.4809363318. These displayed constants are rounded; the engine derives them from canonical definitions. For km/L, L/100km = 100 / (km/L).

• Worked MPG and L/100km guide
• US MPG to L/100km

Compare fuel used over equal distances

For a hypothetical constant consumption, liters used = L/100km × distance in km / 100. Over 1000 km, changing from 15 to 20 US MPG reduces fuel from about 156.8097 L to 117.6073 L: about 39.2024 L saved. Changing from 35 to 40 US MPG reduces fuel from about 67.2042 L to 58.8036 L: about 8.4005 L saved. Both changes add 5 MPG, but their fuel savings differ. These examples describe arithmetic at stated consumption, not advertised vehicle ratings.

Retain rating and measurement context

A unit conversion re-expresses an original rating or measured average. It does not reconcile different test cycles, driving conditions or vehicle configurations. Keep the rating’s original source and context when comparing it with another value. EPA label guidance explains how economy and consumption figures are presented.

• Trip and vehicle unit examples

Separate MPGe from liquid gallons

MPGe expresses distance for an energy quantity equivalent to a gallon of gasoline; EPA uses 33.7 kWh for that equivalence. Ordinary liquid-fuel MPG measures actual gallons and needs no 33.7 kWh constant. EPA electric MPGe includes charging losses at the outlet, so MPGe / 33.7 must not be multiplied by usable battery capacity to derive range.

• MPGe and EV energy accounting
• Calculation methodology

Sources and review

• NIST: named gallon and mile factors
• NIST Handbook 44 Appendix C: customary volume relations and full factors
• EPA/DOE: gasoline label economy and consumption
• EPA: MPGe charging losses and EV range testing
• EPA/DOE: electric vehicle label

Reviewed 2026-10-06. Calculated values are displayed to at most ten significant digits; extra digits do not establish measurement accuracy.