Miles Per Gallon (MPG) Calculator
Work out your car's real-world fuel economy from a trip or a fill-up, see the equivalent L/100km and km/L, cost per mile, and how it compares to typical vehicles.
Enter your numbers
Reset your trip meter at a fill-up, drive until the next fill-up, then enter the miles shown and the gallons it took to fill the tank back up.
Add a fuel price to see cost per mile and an estimated yearly fuel bill.
- Miles used in this calculation
- 300 mi
- Fuel used
- 10 US gal
How you compare
Estimated yearly fuel bill
Based on 12,000 miles a year at 30 mpg and $3.6 per US gallon. Also produces about 3,555 kg of CO2 a year.
Improve your MPG
- Tyre pressure: Underinflated tyres can cut fuel economy by up to 3%.
- Steady speed: Cruise control on the highway smooths out fuel-wasting acceleration.
- Cut the weight: Empty the boot — every extra 45 kg costs roughly 1-2% MPG.
- Regular servicing: A clogged air filter or old spark plugs can quietly drag MPG down.
Good to know
The fill-up method is more accurate than a single trip reading because pump shut-off points vary slightly between fill-ups. For the most reliable figure, average your MPG over 3-4 fill-ups.
About the Miles Per Gallon Calculator
Miles per gallon (MPG) measures how far a vehicle travels on one gallon of fuel — the higher the number, the further it goes and the less you spend at the pump. This calculator works out your real MPG two ways: the trip method, using the distance and fuel shown on a single trip meter reset, and the fill-up method, using two full-tank odometer readings, which most drivers find more accurate over time.
Because a US gallon (3.785 litres) and a UK imperial gallon (4.546 litres) are different sizes, the same car reports a higher "mpg" figure in the UK than in the US for identical real-world fuel use. Switch the unit toggle to match your country, and the calculator also shows the metric equivalent in L/100km and km/L, cost per mile, and an estimated yearly fuel bill.
How to Use the Miles Per Gallon Calculator
- Pick your gallon. US gallon or UK (imperial) gallon — check what your fuel gauge or receipt uses.
- Choose a method. Trip method for a single reset-and-refill; fill-up method if you track your odometer between two full tanks.
- Enter your numbers. Miles driven and gallons used for the trip method, or the two odometer readings and the gallons added at the second fill-up.
- Add a fuel price (optional). Unlocks cost per mile and an estimated yearly fuel bill.
- Set your annual mileage (optional). Defaults to 12,000 miles — change it to match your own driving.
- Read the results. Your MPG, the L/100km and km/L equivalents, cost per mile, and how your car compares to typical vehicle types all update instantly.
Common Use Cases
Checking your car is running efficiently
Log your MPG at every fill-up. A sudden drop can flag a fault before it becomes an expensive repair.
Comparing cars before buying
Convert a manufacturer's L/100km or km/L figure into mpg to compare against a car you already own.
Budgeting for a new commute
Enter your expected annual mileage and local fuel price to see the yearly running cost before you commit.
Rating a used car listing
Sellers often quote optimistic factory MPG — work out the real figure from a test drive's trip computer instead.
Frequently Asked Questions
What's the difference between the trip method and the fill-up method?
The trip method uses your dashboard's trip meter — reset it at a fill-up, then read the miles and gallons at the next one. The fill-up method instead uses the raw odometer, filling the tank completely both times, which removes trip-meter rounding and tends to be the more accurate figure over several tanks.
Why is UK mpg higher than US mpg for the same car?
A UK imperial gallon is about 20% bigger than a US gallon (4.546 vs 3.785 litres), so the same real-world fuel use produces a higher "miles per gallon" number in the UK. Always check which gallon a figure uses before comparing two cars.
How do I convert MPG to L/100km?
For US mpg: L/100km = 235.2 ÷ mpg. For UK mpg: L/100km = 282.5 ÷ mpg. Unlike mpg, a lower L/100km is better — it's litres burned over a fixed distance rather than distance covered per unit of fuel.
Why does my MPG vary between fill-ups?
Weather, traffic, terrain, tyre pressure, payload, and even the pump's auto shut-off point all shift the figure by a few percent. Average several fill-ups for a number you can trust, rather than judging your car from a single tank.
Does this work for diesel or hybrid cars?
Yes — MPG is just distance divided by fuel volume, so it works for petrol, diesel, or hybrid vehicles. Only fully electric cars don't use this measure, since they're priced in cost per kWh rather than cost per gallon.
How is the CO2 figure calculated?
Burning one US gallon of petrol releases about 8.89 kg of CO2 (roughly 20% more per UK gallon, since it holds more fuel). Dividing that by your MPG gives an estimated CO2 output per mile — a tailpipe estimate only, excluding fuel refining and transport.
What counts as a "good" MPG?
It depends on the vehicle type — a hybrid at 50 mpg and a pickup truck at 20 mpg can both be running exactly as designed. The rating badge above compares your figure on a fuel-economy scale (L/100km) so it's consistent regardless of which gallon you use.