Fuel consumption calculator: MPG, trip cost and range

An online tool for calculating fuel consumption from a single fill-up, from a log of several fill-ups, or ahead of a trip. The gas mileage calculator shows MPG, L/100 km and km/L, works out the fuel cost of a trip and each passenger’s share, how many times you will stop for gas on the way, and how many miles are left in the tank.

How to calculate your mileage

1
Miles and gallons

Miles since the last fill-up and gallons from the receipt.

2
Price and passengers

Gas price and how many people are riding.

3
MPG and dollars

MPG, cost per mile and each rider’s share.

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Work out your real gas mileage, what a trip will cost and how far a tank goes

Mileageexample —

How to measure mileage accurately with the full-tank method
  1. Fill the tank until the pump clicks off the first time and reset the trip meter, or write down the odometer.
  2. Drive as usual. The longer, the better: at least half a tank.
  3. Fill up to the first click again, ideally at the same pump, without topping off.
  4. Enter the distance and the gallons from the second receipt: that is the fuel burned over that distance.

The main source of error is topping off to the brim one time and not the next. Several full tanks in a row in the log smooth it out.

The trip will costexample —

Rangeexample —

Range is the fuel in the tank divided by the mileage you entered. City driving, cold weather, the A/C and high speed all lower your mileage, so for those trips enter what your car gets in the same conditions.

Average mileage —

Add at least two fill-ups to a full tank, or open the example.

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Features

The full-tank rule in the log
Fuel is grouped into stretches between two fill-ups to the click: a partial fill-up goes into the next stretch, a stretch with a missed fill-up is left out, and the average is all the fuel over all the distance, not an average of the stretches.
Eight units of consumption
US MPG and UK (imperial) MPG are different numbers: 30 US MPG is 7.8 L/100 km, while 30 UK MPG is 9.4. Also L/100 km and km/L, and for electric cars kWh/100 km, km/kWh, mi/kWh and kWh/100 mi.
Trip cost split among riders
Distance, mileage and price give gallons and dollars; a round trip is one checkbox, the total splits among 2–99 people, and the tank size and reserve show how many gas stops you need.
The margin of error, in numbers
If the tank took 0.13 gal more or less, a 10-gallon fill-up moves the result by ±1.3%. The calculator shows that range under every answer.
A log from your spreadsheet
Paste columns straight from Excel or Google Sheets, with tabs, semicolons or commas. CSV files with headers, including Fuelly and Fuelio exports, are read by column name; you get a CSV and a PDF report with a chart back.
Range from the fuel gauge
Tank size and the needle position (¼, ½, ¾) give gallons in the tank, miles to empty and miles while keeping a reserve, and with a price, what it costs to fill up.

What you can work out

  • Your car’s real gas mileage from a receipt and the odometer
  • What a road trip will cost and how much each passenger should chip in
  • Whether a tank will last to the next gas station on the highway
  • Convert L/100 km from a European review into US MPG
  • A season’s average mileage from a fill-up log with partial fill-ups
  • An electric car’s efficiency in mi/kWh and the cost of a charge

How this calculator is different

Most MPG calculators divide one fill-up’s gallons by the miles and never mention that the answer drifts by a couple of percent depending on when the pump clicked off. With several fill-ups they average the MPG of each, so a short trip around town weighs as much as a thousand highway miles. Here the log works the way drivers who keep records for years do it: only between two full tanks, with partial fill-ups carried into the next stretch and without stretches where a fill-up was never logged. Units are spelled out, because the US and UK gallons differ by a fifth, and there is no “average MPG of model X” without a primary source: only your receipts know your car’s mileage.

Frequently asked questions

Why is my MPG different every fill-up?

The pump clicks off at a slightly different level each time: one fill-up takes a little more, the next a little less. A difference of 0.13 gal on a 10-gallon fill-up moves the answer by 1.3%, on a 5-gallon fill-up by 2.6%. That is why the calculator shows the range under the answer. The more fuel between two full tanks, the more precise it gets, and a log of several fill-ups smooths it out further.

I didn’t fill the tank all the way. How do I count that?

In the log, uncheck “Filled the tank to full.” Those gallons don’t give a mileage of their own: they are added to the next full fill-up, and the mileage is worked out over the whole distance between two full tanks. The single fill-up mode can’t use a partial fill-up, because the gallons on the receipt are then not the fuel burned on that distance.

I forgot to log one fill-up. Is my log wrong now?

Check “Didn’t log the previous fill-up” on the next entry. The stretch where the fill-up went missing is left out of the average entirely: its distance is known but its fuel is not. Without that, the stretch would show mileage that is too good and pull the average up.

Why does the trip computer show a different MPG?

The trip computer never sees the gallons from the pump: it estimates them from how the fuel injectors run, and that estimate can differ from the receipt. The only way to check it is the method used here: fill to full, drive, fill to full again and compare the gallons on the receipt with its number for the same miles.

What is the difference between US MPG and UK MPG?

The gallon: a US gallon is 3.785 liters, an imperial gallon is 4.546 liters. So the same car at 7.8 L/100 km gets 30 MPG in an American review and 36 MPG in a British one. If a review doesn’t say which MPG it uses, go by the country it was published in and pick that unit in the settings.

How do I calculate an electric car’s efficiency?

Switch to “Electric” and enter the kWh from the charger’s meter or your bill, since those are the kilowatt-hours you pay for. The car’s display shows the energy that reached the battery, without charging losses, so its figure looks better. In the log, a “full tank” means charging to your usual level, for example to 80%.

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Who is this tool for?
🚗 Drivers
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