Fuel Tank Range Calculator

How it works

Range is fuel multiplied by fuel economy. A full tank covers its capacity in gallons times the miles per gallon, and whatever is left in the tank covers the gallons left times the same MPG.

Choose whether to describe the fuel left as a gauge reading or in gallons. A gauge reading is converted to gallons as that percentage of the tank capacity, so a quarter tank of a 15-gallon tank is 3.75 gallons.

The reserve is fuel you set aside and do not count on, such as the amount left when the low-fuel light comes on. Miles above reserve are the gallons above that reserve times MPG; when the tank holds no more than the reserve, they are zero.

Formula

full-tank range      = tank capacity × MPG
fuel left (gauge)    = gauge % ÷ 100 × tank capacity
miles remaining      = fuel left × MPG
miles above reserve  = (fuel left − reserve) × MPG     (0 if fuel left ≤ reserve)
full range above reserve = (tank capacity − reserve) × MPG

Example

A 15-gallon tank at 30 mpg covers 15 × 30 = 450 miles when full. With the gauge at a quarter (25%), the tank holds 3.75 gallons, good for 3.75 × 30 = 112.5 miles to empty.

Keeping a 2-gallon reserve, the miles available before reaching it are (3.75 − 2) × 30 = 52.5, and a full tank gives (15 − 2) × 30 = 390 miles above the reserve.

Assumptions and limitations

• Fuel economy is treated as constant for every mile. Real mileage varies with speed, load, terrain, weather and traffic, so the range is an estimate, not a guarantee of how far the vehicle will go.
• Fuel gauges are not linear or exact; many read full for a while after filling and drop faster near empty. A gauge percentage is converted as an exact share of capacity.
• The reserve is a figure you enter. How much fuel remains when a low-fuel warning lights differs by vehicle and is stated in the owner's manual, not assumed here.
• Miles remaining and the full-tank range count every gallon down to empty, as fueleconomy.gov's listed ranges do ("assume 100% of fuel in tank will be used before refueling"). The figures above reserve leave the reserve out.

Frequently asked questions