Gas Mileage Calculator
Calculate fuel economy in mpg and litres per 100 km from distance and fuel used.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Fuel economy depends on distance and fuel used. Select US gallons, imperial gallons or litres; distance is entered in miles. Results are conversions, while the comparison bands are omitted because economy labels depend on vehicle and driving context.
Worked example
calculated with the default values below
Distance driven 320 mi · Fuel used 10 gal · Fuel volume unit US gallons US miles per gallon 32.00 mpg · Imperial miles per gallon 38.43 mpg · Litres per 100 km 7.35 L/100km · Kilometres per litre 13.60 km/L
General background references
Disclaimer
These calculators give estimates for general information only. Real fuel consumption, performance and range vary with driving style, load, terrain, temperature and vehicle condition. Do not rely on these results for towing limits, payload or braking decisions — use the rating plate of your vehicle.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
mpg = d/gal; L100 = gal x 3.785411784 / (d x 1.609344) x 100; km/L = d x 1.609344 / (gal x 3.785411784); mpgUK = d/(gal/1.20095)
- d
- distance (miles)
- gal
- fuel used (US gallons)
- mpg
- US miles per gallon
- mpgUK
- imperial mpg
- L100
- litres per 100 km
- km/L
- kilometres per litre
Fuel is normalized to US gallons. mpg (US) = miles ÷ US gallons; L/100 km and km/L use 3.785411784 L/US gal and 1.609344 km/mile. Imperial gallons are 1.20095 US gallons. These are unit conversions, not a vehicle-efficiency rating.
Frequently asked questions
Why does the same car show a higher imperial MPG?
An imperial gallon is larger than a US gallon. The calculator converts the entered volume to US gallons, then reports both MPG conventions; it also converts the same trip to L/100 km and km/L. The labels describe units only, not whether a vehicle’s economy is good or poor.