How do I measure miles and gallons accurately?

Fill the tank completely, reset the trip odometer, drive normally, then refill to the same full point. The trip odometer gives the distance and the pump shows the gallons added, which is exactly the fuel you used.

What fuel price does the cost-per-mile use?

The cost-per-mile figure assumes a fixed $3.50 per gallon for a quick reference point. To price a specific trip at your local pump price, use the dedicated fuel cost calculator instead.

How do I convert MPG to litres per 100 km?

Divide 235.215 by the MPG value. The constant comes from the number of litres in a US gallon and the kilometres in a mile, and because the metric figure is consumption rather than economy, a lower L/100km number means a more efficient vehicle.

Why does my MPG change between tanks?

Driving style, terrain, traffic, weather, cargo weight, and tyre pressure all move fuel economy up or down. Highway cruising typically returns the best MPG, while short cold trips and heavy city traffic return the worst.

Gas Mileage Calculator

Distance

miles

Fuel Used

gal

MPG30.0

L/100km7.84

Cost per Mile$0.12

This gas mileage calculator measures how efficiently your vehicle uses fuel by dividing the miles you drove by the gallons you burned. It reports the result as miles per gallon (MPG) and converts it to the metric litres-per-100-kilometres figure, plus a rough cost per mile. Tracking MPG across fill-ups helps you spot a drop in efficiency from low tyre pressure, a clogged filter, or a developing engine fault.

Formula

MPG = Distance ÷ Gallons used

Distance: Miles driven on the tank of fuel
Gallons used: Gallons of fuel consumed (must be positive)
MPG: Fuel economy in miles per gallon
L/100km: Metric consumption = 235.215 ÷ MPG

How it works

Drive on a full tank, then at your next fill-up record the miles travelled (from the trip odometer) and the gallons it took to refill.
Enter the distance in miles and the gallons used; the calculator divides miles by gallons to compute MPG.
It also converts MPG to litres per 100 km using 235.215 ÷ MPG and estimates cost per mile at an assumed $3.50 per gallon.

Worked example

A driver covered 350 miles and refilled with 12 gallons of fuel.

MPG: 350 ÷ 12 = 29.17 miles per gallon.
Metric: 235.215 ÷ 29.17 = 8.06 L/100km.
Cost per mile at $3.50/gal: 3.50 ÷ 29.17 = $0.12.

Fuel economy is about 29.17 MPG, equal to 8.06 L/100km and roughly $0.12 per mile.

Frequently asked questions

How do I measure miles and gallons accurately?: Fill the tank completely, reset the trip odometer, drive normally, then refill to the same full point. The trip odometer gives the distance and the pump shows the gallons added, which is exactly the fuel you used.
What fuel price does the cost-per-mile use?: The cost-per-mile figure assumes a fixed $3.50 per gallon for a quick reference point. To price a specific trip at your local pump price, use the dedicated fuel cost calculator instead.
How do I convert MPG to litres per 100 km?: Divide 235.215 by the MPG value. The constant comes from the number of litres in a US gallon and the kilometres in a mile, and because the metric figure is consumption rather than economy, a lower L/100km number means a more efficient vehicle.
Why does my MPG change between tanks?: Driving style, terrain, traffic, weather, cargo weight, and tyre pressure all move fuel economy up or down. Highway cruising typically returns the best MPG, while short cold trips and heavy city traffic return the worst.

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