Gas Mileage Calculator (MPG)
Calculate miles per gallon from miles driven and gallons used, average several trips at once, and convert to L/100 km and km/L.
Result
- Total miles300.0
- Total gallons (US)12.000
- MPG (US)25.00
- MPG (imperial / UK)30.02
- L/100 km9.41
- km per litre10.63
Step-by-step
- Total the miles: 300 = 300.0 mi.
- Total the gallons: 12 = 12.000 gal.
- MPG = 300.0 ÷ 12.000 = 25.00 miles per gallon.
- Convert: 235.214583 ÷ 25.00 = 9.41 L/100 km.
How to use this calculator
- Enter the miles driven (or a comma-separated list of several trips).
- Enter the US gallons used (one value, or a matching list for multi-trip averaging).
- Read your MPG plus L/100 km, km/L, and imperial MPG equivalents.
- For the best accuracy, measure brim-to-brim and average several tanks.
About this calculator
Miles per gallon (MPG) is the simplest measure of fuel economy: the distance your vehicle travels on one US gallon of fuel. To get it, divide the miles driven by the gallons used to cover them. The most accurate way to measure is brim-to-brim — fill the tank completely, reset the trip meter, drive normally, then refill and note the gallons it took. This calculator also averages multiple trips: enter comma-separated lists of miles and gallons and it totals both before dividing, which gives a more representative figure than any single tank. Results are also shown in the metric L/100 km and km/L units, and in imperial (UK) MPG, which is about 20% higher than US MPG because the imperial gallon is larger.
How it works — the formula
MPG (US) = Total miles ÷ Total US gallons
L/100 km = 235.214583 ÷ MPG
km/L = MPG × 0.425143707
MPG (UK) = MPG (US) × 1.200949925Fuel economy is distance divided by fuel. Multi-trip averaging sums distances and fuel separately so each trip is weighted by how far it was, not equally.
Worked examples
- Inputs:
- miles=300, gallons=12
- Output:
- 300 ÷ 12 = 25.0 MPG (9.41 L/100 km)
- Inputs:
- miles=400, gallons=10
- Output:
- 40.0 MPG
- Inputs:
- miles=300,280; gallons=12,11
- Output:
- 580 ÷ 23 = 25.2 MPG
Limitations
- Uses US gallons; convert metric data first or read the km/L output.
- Single-tank figures vary; averaging tanks is more reliable.
- Does not account for fuel grade or hybrid battery contribution.
Measured economy varies with conditions; brim-to-brim averaging gives the truest figure.