Fuel Economy / Gas Mileage Converter

What this fuel economy converter does

US car specs are in miles per gallon, most of the rest of the world uses liters per 100 kilometers (where, confusingly, a lower number means better efficiency), and UK sources sometimes throw in Imperial MPG on top, which isn't the same gallon as the US one. This tool converts between all five units car shoppers and travelers actually run into — MPG (US), MPG (UK/Imperial), L/100km, km/L, and mi/L — updating every field at once from whichever one you enter.

It also answers the question a plain unit converter can't: what will a trip actually cost? Enter a distance and your local fuel price, and it calculates how much fuel you'll burn and what it'll cost, using the same fuel-economy figure you just converted.

How to use it

Enter your car's fuel economy figure and pick its unit — from a spec sheet, a rental car listing, or a friend's "my car gets 8 L/100km" — and every other unit updates instantly. For the trip cost estimate below, add your distance (miles or km) and local fuel price per gallon or per liter, and you'll get the fuel needed and the estimated cost for that trip.

A real example

A US car rated at 30 MPG converts to about 7.84 L/100km, 12.75 km/L, and 25.0 MPG on the UK/Imperial scale (Imperial gallons are about 20% larger than US gallons, so the same fuel-per-distance ratio yields a lower Imperial MPG number, not a higher one — a common point of confusion). For a 300-mile trip at $3.50/gallon, that same car needs about 10 gallons and costs roughly $35.

Frequently asked questions

Why is UK MPG different from US MPG for the same car?

They're not actually different fuel economy — it's a different-sized gallon doing the measuring. An Imperial (UK) gallon is about 4.55 liters versus 3.79 liters for a US gallon, so converting the same real-world fuel economy into "miles per Imperial gallon" gives a lower number than "miles per US gallon," even though nothing about the car changed.

Why does L/100km work backwards from MPG?

MPG measures distance per unit of fuel (bigger is better); L/100km measures fuel per unit of distance (smaller is better). They're inverse relationships, which is exactly why this tool converts between them with a reciprocal formula rather than a simple multiplier.

Does this account for hybrid or electric vehicles?

No — this converter is for internal-combustion fuel economy figures. Electric vehicle efficiency is typically measured in miles/kWh or kWh/100km, a different kind of unit entirely.

How accurate is the trip cost estimate?

It's a straight-line calculation from your entered fuel economy, distance, and price — real-world consumption varies with terrain, driving style, traffic, and load, so treat it as a solid planning estimate rather than an exact figure.

Can I use this for motorcycles, trucks, or boats?

Yes — the unit conversions and trip cost math work the same regardless of vehicle type, as long as you have a fuel economy figure in one of the five supported units to start from.