Fuel Distance Calculator works out the miles left on the fuel in your tank at your MPG, the range before your chosen reserve, and whether that fuel reaches the place you are going.
How the Fuel Distance Calculator Finds Your Range
The Fuel Distance Calculator works out how far you can drive on the fuel in your tank. It also checks whether that fuel reaches a destination while leaving a reserve, and how long the fuel lasts at your average speed.
Enter your tank size and pick a fuel gauge reading, or type the exact amount of fuel on hand. Then add the fuel you want to keep in reserve, your fuel economy, your average speed and the distance to your destination.
Fuel can be entered in US gallons, liters or UK gallons. Fuel economy can be MPG (US), MPG (UK), L/100 km or km/L, and distance can be miles or kilometers.
The Fuel Distance Calculator Formula
Range is fuel times fuel economy. With the fuel in gallons and economy in MPG, the answer comes out in miles.
$$\text{Range} = \text{Fuel on hand} \times \text{Fuel economy}$$
With the defaults, a 15-gallon tank at 3/4 holds 11.25 gallons. At 24 MPG, that is 270 miles until the tank runs dry.
When economy is entered as L/100 km, the Fuel Distance Calculator inverts it first, since that unit states fuel per distance rather than distance per fuel. Internally, every entry becomes liters and kilometers, using 3.785411784 liters per US gallon and 1.609344 km per mile.
A common mistake is using the EPA highway rating for mixed driving. The combined figure, or your own average from a few fill-ups, gives a range you can count on.
Range Before You Hit Your Reserve
Driving to empty is not a plan, so the first result card subtracts the reserve you set. With 1.5 gallons held back, the default tank covers 234 miles before you touch the reserve.
$$\text{Usable range} = (\text{Fuel on hand} – \text{Reserve}) \times \text{Fuel economy}$$
The same card shows how far the reserve itself would carry you, 36 miles here. It also repeats the total range in the other distance unit, 435 km at the defaults.
How Much Is Left When the Fuel Light Comes On
AAA’s Car Doctor John Paul says most cars have about 1 to 2 usable gallons left when the low fuel light comes on. In his test drives, most cars went 30 to 50 miles after the light.
The reserve field defaults to 1.5 gallons, the middle of that range. The alert box turns that 1 to 2 gallon range into miles at your own fuel economy, which is 24 to 48 miles at 24 MPG.
AAA also describes a way to find your own car’s number. Fill the tank, drive until the light comes on, and note the miles. Refill, then subtract the gallons you pumped from the tank size.
What remains is the fuel left at the light. Enter it as your reserve, and the Fuel Distance Calculator will show your range to the light instead of to empty.
Will the Fuel Reach Your Destination?
In the second card, the Fuel Distance Calculator compares your usable range with the distance you enter. For the default 200 miles, it shows 34 miles to spare, 8.33 gallons used, and 2.92 gallons left on arrival.
If the distance is longer than your usable range, the card switches to show how far short you fall. It then counts the fill-ups you will need, assuming each fill brings the tank back to full.
Try 500 miles with the defaults. You come up 266 miles short, and one fill-up covers the gap. The alert tells you to refuel within 234 miles and says each later tank covers about 324 miles before the reserve.
To see what that fuel will cost, the fuel cost calculator prices any distance from your MPG and the pump price.
Drive Time and Fuel Burned per Hour
The third card of the Fuel Distance Calculator turns range into time. At 60 mph, the 234 usable miles last 3 hr 54 min, and a full tank down to the reserve lasts 5 hr 24 min.
It also shows fuel burned per hour, which is speed divided by fuel economy. At 60 mph and 24 MPG, that is 2.50 gallons per hour.
Speed only affects the time results. It does not change fuel economy in the math, so enter the MPG you actually get at the speed you plan to drive.
MPG, L/100 km and UK Gallons
The fourth card restates your fuel economy in the other rating units. At the defaults, 24 MPG (US) equals 9.80 L/100 km, 10.20 km/L and 28.82 MPG (UK).
The UK gallon holds 4.54609 liters, about 20% more than a US gallon, so UK MPG figures run higher for the same car. If your rating is in km/L from distance and liters you logged, the liter to km calculator works it out first.
Limits and Alerts
Tank size, fuel economy, speed and distance must all be greater than zero. Fuel on hand and the reserve can be zero, but not negative.
The reserve must be smaller than the tank, or the Fuel Distance Calculator flags it. When the fuel on hand is at or below the reserve, the alert turns red and shows the miles left until empty.
If you enter more fuel than the tank holds, a yellow alert asks you to check the entries. That result still works when you carry spare fuel cans.
The gauge menu treats each mark as an exact fraction of the tank. A needle is only an estimate, so switch to Custom Amount when you know the real number of gallons.
Range Mistakes to Avoid
Entering the tank size from memory can throw off every result in the Fuel Distance Calculator. Check the owner’s manual, since the stated capacity is the number the gauge fractions are based on.
Mixing US and UK gallons skews range by about 20%. Set the fuel unit to Gal (UK) if your figures come from a British or Irish source.
Leaving the reserve at zero shows range to a dry tank. Set a reserve so the plan leaves you fuel to reach a station.
Driving Range Questions
How far can I drive on a full tank?
Multiply the tank size by your fuel economy. A 15-gallon tank at 24 MPG goes about 360 miles to empty. Keep 1.5 gallons in reserve and the usable range drops to 324 miles. Set the gauge to Full in the Fuel Distance Calculator to see both numbers, along with how long a full tank lasts at your speed.
How many miles can I drive after the gas light comes on?
Most cars can go 30 to 50 miles, according to AAA, because about 1 to 2 usable gallons remain. The exact figure depends on your car and your fuel economy. At 30 MPG, 1.5 gallons covers about 45 miles. Treat the light as a signal to refuel, not as extra range to plan around.
How many gallons is a quarter tank?
Divide the tank size by four. A 15-gallon tank at 1/4 holds about 3.75 gallons, and a 20-gallon tank holds about 5. At 24 MPG, 3.75 gallons covers about 90 miles to empty. Fuel gauges are approximate, so the real amount can differ from the needle.
Why does my dashboard range differ from the calculator?
Your car’s distance-to-empty display usually estimates range from your recent fuel economy. It changes as your driving changes, such as a stretch of city traffic or highway cruising. The calculator uses the single MPG you enter. Enter the economy you expect for the drive ahead, and set a reserve, to get a figure you can plan around.