MPG Calculator
MPG calculator: real miles per gallon from fill-up data, with cost per mile, metric units and a two-car comparison. Free, no sign-up, and it runs in your browser.
Dedicated page: /en/mpg-calculator
Default checked 10 Nov 2026: $4.01 (AAA national average for regular, 9 Nov 2026). Enter your local price. Check the current value here.
Leave 0 to skip the comparison.
Fill the tank, drive, fill it again, and divide the miles by the gallons it took: that is your real MPG, not the EPA sticker figure. Dashboard readings usually read 3% to 8% optimistic.
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Quick answer
An MPG calculator works out your real fuel economy from fill-up data. Divide the miles you drove by the gallons you used, and it shows miles per gallon in US and UK gallons, litres per 100 km, kilometres per litre, the cost per mile at your gas price, and the yearly fuel cost.
About this MPG Calculator
MPG calculator: real miles per gallon from fill-up data, with cost per mile, metric units and a two-car comparison. It is one of the Car and Travel on ToolUstad, and like every tool here it runs entirely in your browser: nothing you type, paste or open is uploaded to a server, and there is no sign-up or usage limit.
What is an MPG calculator?
MPG, miles per gallon, is the miles a car travels on one gallon of fuel, and it is the standard fuel-efficiency measure in the United States. The only reliable way to know your car number is to measure it: fill the tank, drive, fill it again, and divide the distance by the fuel it took to refill. Driving 320 miles on 11.5 gallons is 27.83 MPG. At $4.01 a gallon, the fill-up costs $46.11 and each mile costs $0.14.
Four modes cover the ways people actually measure. One fill-up is the quickest: miles and gallons. Odometer readings use the two readings and the gallons at the second fill-up. Several fill-ups averages total miles over total gallons across up to three fill-ups. City and highway mode combines two ratings with the EPA formula, 55 percent city and 45 percent highway, so 24 city and 32 highway becomes 27.04 MPG combined.
US gallons, UK gallons and metric units
The conversions come from three exact definitions: 1 mile is 1.609344 km, 1 US gallon is 3.785411784 litres, and 1 imperial gallon is 4.54609 litres. An imperial gallon is 20.1 percent larger than a US gallon, so the same car always reads about 20 percent higher in UK MPG: multiply US MPG by 1.201. Litres per 100 km is 235.215 divided by US MPG, and it is the figure most of the world uses.
What your MPG costs you
Fuel cost per mile is the gas price divided by MPG, so a 27.83 MPG car at $4.01 a gallon costs $0.14 a mile. Over 12,000 miles a year that is 431 gallons and $1,729. The comparison table on this page runs the same maths for 15 to 50 MPG, and the two-car comparison shows the yearly saving directly: a 35 MPG car costs $1,374.86 for the same 12,000 miles, saving $354.46 a year.
Your real MPG differs from the sticker because the EPA tests in a laboratory under controlled conditions. Highway speed above 50 mph, air conditioning, cold starts, short trips, extra load and low tyre pressure all cut it.
Best practices
- Fill to the same level every time: stop at the first pump click, so each fill-up is comparable.
- Average three or more fill-ups: one fill-up can be off by a gallon if the pump clicks early.
Common mistakes to avoid
- Trusting the dashboard readout, which usually reads 3 to 8 percent optimistic.
- Mixing US and UK gallons, which makes a car look 20 percent better than it is.
- Using the highway rating for a yearly budget, when most miles are mixed driving.
Who is the MPG calculator for?
Drivers checking their real fuel economy, buyers comparing two cars, and anyone budgeting yearly fuel costs. It pairs with the fuel cost calculator on this site for trip costs, and the road trip cost calculator for full holiday budgets.
Current value, checked 10 Nov 2026: the default gas price is $4.01, the AAA national average for regular gasoline as of 9 Nov 2026. The price box is an optional override. Check the current value here.
Learn: how to use the MPG Calculator
- Pick how to measure: one fill-up, odometer readings, several fill-ups averaged, or city and highway ratings.
- Enter the miles and gallons, or the two odometer readings and the gallons at the next fill-up.
- Enter the gas price to see the cost per mile and the fill-up cost.
- Enter your yearly miles and a second car MPG to compare annual fuel costs.
- Read your MPG in US, UK and metric units, plus the comparison table for 15 to 50 MPG.
Features
- Four modes: single fill-up, odometer, multi fill-up average, city and highway
- US MPG, UK MPG, litres per 100 km, km per litre and gallons per 100 miles
- Cost per mile and per fill-up at your gas price
- Annual fuel cost from your yearly miles
- Two-car comparison: yearly saving of the more efficient car
- Tank range and a conversion table for 15 to 50 MPG
Worked example
Driving 320 miles on 11.5 gallons is 27.83 MPG in US gallons, 33.42 MPG in UK gallons, 8.45 litres per 100 km, 11.83 km per litre, and 3.59 gallons per 100 miles. At $4.01 a gallon the fill-up costs $46.11 and each mile costs $0.14. Over 12,000 miles a year the car burns 431 gallons and costs $1,729 in fuel. A 35 MPG car costs $1,374.86 for the same miles, saving $354.46 a year.
Frequently asked questions
How do I calculate MPG?
Divide the miles you drove by the gallons you used. Fill the tank, drive, fill it again, and use the pump reading as the gallons: 320 miles divided by 11.5 gallons is 27.83 MPG.
Why is my real MPG lower than the EPA rating?
EPA ratings come from standardised lab cycles, and real driving adds highway speed, air conditioning, stop-start traffic, cold starts and extra load. Real-world MPG usually runs a few percent below the rating, and dashboard readings usually read 3 to 8 percent optimistic.
What is the difference between US MPG and UK MPG?
An imperial gallon is 4.546 litres and a US gallon is 3.785 litres, so the imperial gallon is 20.1 percent larger. The same car travels 20 percent more miles per UK gallon, so multiply US MPG by 1.201 to get UK MPG.
How do I convert MPG to litres per 100 km?
Divide 235.215 by the US MPG figure. 30 MPG is 7.84 litres per 100 km, 40 MPG is 5.88, and 50 MPG is 4.70.
What is a good MPG?
Anything above the roughly 24 MPG average of a new US car is good. Compact sedans typically get 30 to 40 MPG on the highway, SUVs and trucks 15 to 25 MPG, and hybrids 45 to 57 MPG.
Should I use city or highway MPG for my budget?
Use the combined figure for a yearly budget: the EPA formula is 55 percent city and 45 percent highway. On 24 city and 32 highway, combined is 27.04 MPG. Use highway MPG only for a long road trip, and city MPG only for short urban driving.
How many fill-ups should I average?
At least three. One fill-up can be off if the pump clicks early or late, or the tank was not filled to the same level.
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