Maintenance & Fuel · Free tool
Free MPG Calculator
Enter the miles you drove between two fill-ups and the gallons it took to refill. The calculator gives your real fuel economy and what each mile costs.
- Free to use
- No signup
- Runs in your browser
Between two fill-ups
Fill to the brim both times. The pump receipt gives the gallons.
Over a year
Your fuel economy
28.1 MPG
320 miles on 11.4 gallons.
- Liters per 100 km
- 8.4
- Kilometers per liter
- 11.9
- Fuel cost per mile
- $0.12
- Fuel cost per 100 miles
- $12
- Cost of this tank
- $39.90
- Fuel cost per year
- $1,496
One tank is a snapshot. Average three or four fill-ups for a figure you can rely on.
An estimate from the figures you enter, not a quote. Read the disclaimer. Updated .
02Your result
What your MPG result means
MPG is how far the car travels on one gallon. Measured at the pump, it is the truest figure you can get.
- 01
Miles per gallon
Your fuel economy over that tank. Higher is better. Compare it with the car’s rated MPG and with your own past results.
- 02
Cost per mile
The price of a gallon divided by your MPG. It turns fuel economy into money, which is how to compare two cars.
- 03
Liters per 100 km
The metric measure, which runs the other way: a lower number is better. The calculator converts it for you.
What to do next
Cost a trip
Use your real MPG to work out the fuel for a journey or a year of driving.
Fuel cost calculatorImprove the number
The driving and maintenance habits that move fuel economy most.
Fuel economy guideCheck your tire pressure
Under-inflated tires waste fuel. See what a cold snap does to your pressures.
Tire pressure calculator
03How it works
The MPG formula
Fuel economy is distance divided by fuel. Everything else on the results panel comes from that one figure.
MPG = miles driven ÷ gallons used
L/100 km = 235.215 ÷ MPG. Cost per mile = price per gallon ÷ MPG
235.215 is the NIST conversion factor between US miles per gallon and liters per 100 kilometers.
What each term means
- miles driven
- The distance between two fill-ups, from the trip meter or two odometer readings.
- gallons used
- The fuel it took to refill the tank at the second fill-up, in US gallons.
- MPG
- Miles per US gallon.
- L/100 km
- Liters of fuel used to travel 100 kilometers.
What the tool assumes
- The tank was filled completely both times.
- US gallons and statute miles.
- The price you enter is what you paid for that fuel.
- Yearly cost assumes your fuel economy and the price stay the same all year.
04Worked example
MPG example: 356.2 miles on 13.5 gallons
The example fueleconomy.gov uses: a car that covers 356.2 miles between fill-ups and takes 13.5 gallons to refill, with fuel at $3.50 a gallon.
- 01
Note the distance
Second odometer reading minus the first
356.2 miles
- 02
Note the fuel
Gallons shown on the pump at the second fill-up
13.5 gal
- 03
Divide
356.2 ÷ 13.5
26.4 MPG
- 04
Convert to metric
235.215 ÷ 26.4
8.9 L/100 km
- 05
Work out the cost per mile
$3.50 ÷ 26.4
$0.13
Fuel economy
26.4 MPG
At $3.50 a gallon that is $0.13 a mile, or about $1,592 for 12,000 miles of driving.
Try your own numbers05Background
How to calculate MPG by hand
The method the U.S. Department of Energy and the EPA describe on fueleconomy.gov needs nothing but two fill-ups and a note of the mileage.
- 01
Fill the tank completely
Record the odometer reading, or reset the trip meter.
- 02
Drive as you normally do
The longer the distance, the more reliable the result.
- 03
Fill the tank completely again
Record the gallons it took and the new odometer reading.
- 04
Divide miles by gallons
Subtract the first reading from the second, then divide by the gallons added.
One tank is a snapshot. A single fill-up can be thrown off by a pump that clicks off early or by an unusual week of driving, so average three or four tanks before you draw a conclusion.
A sudden fall in MPG with no change in how you drive is a symptom, not a statistic. Low tire pressure, a dragging brake or a failing sensor can all cause it. See the fuel economy section of the maintenance guide for what to check.
06When to use it
When to use an MPG calculator
The dashboard readout is an estimate. A pump-to-pump calculation is a measurement.
To spot a problem early
Track MPG tank by tank. A sustained drop is often the first sign of a fault.
To check the car’s rating
Compare your real figure with the EPA rating for your model.
To budget for fuel
Turn MPG into a cost per mile and a yearly fuel bill.
Before a long trip
Use a measured highway MPG, not the brochure figure, to plan fuel stops.
Mistakes to avoid.
- Topping off to different levels at the two fill-ups, which changes the gallons figure.
- Judging the car on a single tank.
- Mixing units, such as kilometers driven with gallons used.
- Trusting the trip computer without ever checking it against the pump.
07Related guides and tools
Keep going from here.
Guides that go with this tool
08Questions
MPG Calculator: your questions.
How do I calculate MPG?
Divide the miles you drove by the gallons it took to refill the tank. Fill up, note the odometer, drive, fill up again and note the gallons and the new reading. For example, 356.2 miles on 13.5 gallons is 26.4 MPG.
How do I convert MPG to L/100 km?
Divide 235.215 by the MPG figure. A car that does 30 MPG uses 7.8 liters per 100 kilometers. To convert the other way, divide 235.215 by the L/100 km figure.
How do I work out fuel cost per mile?
Divide the price of a gallon by your MPG. At $3.50 a gallon and 28 MPG, fuel costs 12.5 cents a mile.
Why is my MPG lower than the car’s rating?
Rated figures come from standard tests. Short trips, high speeds, cold weather, heavy loads and under-inflated tires all lower real-world fuel economy.
Is the MPG on my dashboard accurate?
It is an estimate calculated by the car. Check it against a pump-to-pump calculation over a few tanks to see how far it is out for your vehicle.
09Estimates and sources
Read this before you rely on it.
Built and checked by CarTipsMentor Team. Last updated . How we check our work.
Sources
- [1]fueleconomy.gov (U.S. Department of Energy and EPA), Calculating Your MPG
- [2]National Institute of Standards and Technology, NIST Guide to the SI, Appendix B.9: conversion factors
- [3]fueleconomy.gov (U.S. Department of Energy and EPA), Driving More Efficiently
- [4]fueleconomy.gov (U.S. Department of Energy and EPA), Keeping Your Vehicle in Shape