How to use the distance on a tank calculator
- Pick the units: gallons and MPG, or liters and L/100 km.
- Enter the tank size and your fuel economy. Optionally enter the fuel you keep in reserve.
- Enter how full the tank is now, as a percent.
- Optionally enter a trip distance. Read the range on a full tank, the range from the fuel in the tank now and whether it covers the trip.
Formula
US units: range = fuel in gallons x miles per gallon
Metric units: range = fuel in liters / (liters per 100 km) x 100
Usable range = (tank size - reserve) x the same economy
Fuel in the tank = tank size x fill level %
Fuel needed for a trip = distance / MPG, or distance x L/100 km / 100
Kilometers per liter is 100 divided by liters per 100 km.
A 14-gallon tank at 28 MPG
A full tank gives 14 x 28 = 392 miles. Keeping 2 gallons in reserve cuts the usable range to 12 x 28 = 336 miles. At half a tank (7 gallons) the range is 196 miles, and a 300-mile trip would need 10.71 gallons, so the half tank would fall short.
In metric units, a 50-liter tank at 8 L/100 km gives 50 / 8 x 100 = 625 km. Both examples use values you can replace with your own.
Where the number comes from
Range is fuel multiplied by distance per unit of fuel. In MPG, a bigger number is better. In L/100 km, a smaller number is better, which is why the formula divides. The tool converts for you and shows kilometers per liter as well.
Use the fuel economy you actually get, which is usually a mix of city and highway. The rated figure may differ from your real mileage, and the MPG calculator helps you measure yours from fill-ups.
Why a margin matters
Fuel gauges are not exact, and the last part of a tank is not a safe place to plan around. Speed, load, weather, hills and air conditioning all change economy. The reserve box is for the fuel you never plan to use.
To price a trip use the fuel cost calculator. For propane tanks see the propane tank runtime calculator, and to compare an electric vehicle with gas try the EV vs gas cost calculator.
Assumptions and limits
- Fuel economy is steady for the whole distance.
- The tank size is the usable capacity you enter.
- The tank level is a percent of the full tank.
- Gauge error, driving conditions and fuel cost are not modeled.
Frequently asked questions
How far can I drive on a tank of gas?
Multiply the tank size in gallons by your miles per gallon. A 14-gallon tank at 28 MPG gives 392 miles.
How do I calculate range in liters per 100 km?
Divide the liters in the tank by the liters per 100 km and multiply by 100. A 50-liter tank at 8 L/100 km goes 625 km.
Should I count the last gallon?
That is your decision. Use the reserve box to remove fuel you do not plan to use, and the usable range shows what is left.
Why is my real range shorter than the result?
Mileage changes with speed, traffic, load and weather, and gauges are approximate. Use your own measured economy and leave a margin.