About the MPG Calculator
This MPG calculator works out your vehicle’s actual fuel economy from a tank of driving. Enter the distance you drove and the fuel it took to refill, and it calculates miles per gallon (US), plus the metric equivalents — litres per 100 km and km per litre — and imperial (UK) miles per gallon. Add the price you paid for fuel to see the cost per mile and per kilometre.
The most accurate method is the fill-to-fill approach: fill the tank completely, reset the trip odometer, drive as normal, then fill up again and note the miles and gallons. Averaging over several tanks smooths out differences in how full the pump stops. You can enter miles and US gallons or kilometres and litres.
Tracking MPG over time helps you spot problems early — a sudden drop can point to under-inflated tyres, a dragging brake, a failing oxygen sensor or a clogged air filter. It also lets you compare your real-world figure with the EPA rating on the window sticker and budget accurately for fuel.
With the default inputs, the miles per gallon (us) is 28 mpg. Change any value above to recalculate instantly.
How to use the mpg calculator
- 1Fill your tank completely and reset the trip odometer.
- 2Drive normally until you next need fuel, then fill the tank again.
- 3Choose your units and enter the distance on the trip meter.
- 4Enter the fuel it took to refill and the price you paid.
- 5Read your MPG and the metric and UK equivalents.
Formula and method
Miles per gallon is the distance driven divided by the fuel used. If you enter kilometres and litres, the calculator first converts them using 1 mile = 1.609344 km and 1 US gallon = 3.785411784 litres. Litres per 100 km is fuel ÷ distance × 100 — note it moves the opposite way to MPG, so a lower number is better.
UK (imperial) MPG uses the larger 4.54609-litre imperial gallon, so the same car shows about 20% higher MPG in the UK. Fuel cost is the fuel used multiplied by the price per unit, and cost per mile or kilometre divides that by the distance.
- MPG
- Miles per US gallon
- L/100 km
- Litres of fuel used per 100 kilometres
Worked examples
350 miles on 12.5 gallons
350 ÷ 12.5 = 28 mpg, which is about 8.4 L/100 km or 33.6 UK mpg. At $3.40 a gallon the tank cost $42.50, or about 12¢ per mile.
Hybrid: 412 miles on 10.3 gallons
412 ÷ 10.3 = 40 mpg, or 5.9 L/100 km. At $3.59 a gallon the fill-up cost $36.98, just under 9¢ a mile.
Metric: 600 km on 42 litres
42 litres over 600 km is 7.0 L/100 km (14.3 km/L), equal to 33.6 US mpg or 40.4 UK mpg. At 1.75 per litre the fuel cost 73.50, about 0.12 per km.
Frequently asked questions
How do I calculate my MPG?+
Fill the tank, reset the trip odometer, and drive until your next fill-up. Refill to full, then divide the miles driven by the gallons you added. For example, 300 miles ÷ 10 gallons = 30 mpg.
What is good gas mileage?+
For a gasoline car, about 30 mpg or more combined is generally considered good today, while many hybrids exceed 45–50 mpg. Pickup trucks and large SUVs commonly achieve 15–25 mpg. Compare with the EPA rating for your specific model.
How do I convert MPG to L/100 km?+
Divide 235.215 by the US MPG figure. So 30 mpg is about 7.8 L/100 km and 40 mpg is about 5.9 L/100 km. For UK mpg divide 282.481 by the figure instead.
Why is my real MPG lower than the EPA rating?+
Short trips, cold weather, idling, high highway speeds, aggressive acceleration, under-inflated tyres, roof racks and heavy loads all reduce fuel economy. EPA figures are measured under standardised test conditions, so real-world results often differ.
Sources