Fuel Economy Converter

Convert between MPG, L/100km, and km/L fuel consumption units with trip cost estimation.

Tested tool guide Tested browser tools Checked August 16, 2026

What Fuel Economy Converter does, with a checked example

Fuel Economy Converter translates a consumption or distance-per-fuel figure among miles per gallon (MPG), liters per 100 kilometers (L/100km), and kilometers per liter (km/L), then applies the selected economy to a trip distance and fuel price. The important surprise is direction: higher MPG and km/L mean better economy, while lower L/100km means better economy. MPG is also ambiguous unless its gallon basis is identified, so verify whether a source uses US or Imperial gallons.

Worked example

A concrete input and expected output from the current implementation.

Input

Economy: 10 L/100km
Trip distance: 100 km
Fuel price: $2.00/L

Expected output

Equivalent economy: 23.52 MPG (US), 10.00 km/L. Trip fuel: 10.00 L. Trip cost: $20.00.

At 10 L per 100 km, a 100 km trip uses exactly 10 L. Dividing 235.214583 by 10 gives 23.5214583 US MPG, which rounds to 23.52, while 10 L multiplied by $2.00/L gives $20.00.

How the result is produced

Reciprocal conversion

MPG and km/L are distance-per-volume measures, so they rise as economy improves. L/100km is fuel-per-distance and moves oppositely. Converting a distance-per-volume value to L/100km requires a reciprocal: for US MPG, L/100km equals 235.214583 divided by MPG. Likewise, km/L equals 100 divided by L/100km.

Trip calculation

Trip estimation first expresses distance and economy in compatible units. Fuel required is trip distance divided by MPG or km/L, or trip kilometers multiplied by L/100km and divided by 100. Estimated cost is that fuel quantity multiplied by a price per matching gallon or liter. Volume and price units must agree before multiplication.

Good uses

Comparing a Canadian vehicle listing stated in L/100km with a US listing stated in MPG.
Translating a dashboard's km/L reading into L/100km for a maintenance or fleet record.
Estimating fuel volume and cost for a planned drive from its distance, expected economy, and pump price.

Limits and checks

Confirm which gallon MPG means. US MPG and Imperial MPG use different gallon volumes, so the same MPG number cannot represent both.
Treat the estimated cost as being in the same currency as the entered fuel price; the calculation does not imply a currency exchange rate.
A single economy figure is only an estimate. Traffic, speed, temperature, terrain, load, idling, and driving style can change actual consumption.

Common questions

Why does lower L/100km correspond to higher MPG?

They express opposite ratios. MPG asks how far one gallon moves the vehicle, so larger is better. L/100km asks how much fuel is consumed over a fixed distance, so smaller is better. Their relationship is reciprocal: halving L/100km doubles the corresponding MPG when the same gallon definition is used.

Can I use an Imperial MPG figure as US MPG?

No. US and Imperial MPG are not interchangeable because their gallons have different volumes. If the MPG label uses US gallons, first convert an Imperial figure or start from an available L/100km or km/L value. Do not infer the gallon basis from the numeric value or the vehicle's country alone.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.