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Fuel Tank Range Calculator

Estimate how far you can drive on the fuel left in your tank, from the gauge or the amount and your fuel economy. See if a trip will fit.

Level: Grade 6

Printable worksheet

Fuel Tank Range Calculator

Know the answer you need? Pick an input to work backward.

Inputs
Fuel left, from

¼ tank = 25%, ⅛ = 12.5%, ½ = 50%.

Your real-world average, ideally from the trip computer or a recent fill-up.

Range held back for gauge error, hills, traffic and finding a station.

Show distance in

In the distance unit chosen above.

Result

Estimated range

98 mi

With 3.5 US gal left, you can drive about 98 mi (88.2 mi keeping a 10% margin).

Range in kilometers
157.7 km
Fuel left
3.5 US gal
Range keeping a 10% margin
88.2 mi

See the step-by-step solution ↓

Step-by-step solution

  1. Fuel left: tank size times the gauge reading

    14 US gal×25%=3.5 US gal

  2. Range: fuel left times the distance per US gal

    3.5×28=98 mi

  3. Hold back 10% of the range as a safety margin

    98 mi×(1−10%)=88.2 mi

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

Please note: Results are estimates for planning and comparison. Lenders, banks, and tax authorities may round differently or include fees not modeled here, so confirm figures with your provider before deciding.

What this calculator does

Find out how far you can drive on the fuel left in your tank, and whether you'll make your next stop. Say the needle is near a quarter and the next town is 60 miles away. Meanwhile, the dashboard's distance-to-empty figure jumps around every time the road tilts. The math underneath is easy. Take the fuel you have, times the distance your vehicle goes on each gallon or liter. Doing it yourself, with your real fuel economy and a sensible margin, gives a steadier answer.

You can start from the gauge reading and the tank size. Or start from the amount of fuel you know is in the tank. Fuel economy can be in US or imperial miles per gallon, liters per 100 km, or kilometers per liter. The calculator gives your range in miles or kilometers, plus the range left after a safety margin. If you enter the distance still to drive, it tells you whether you can make it. If not, it tells you how much fuel to add.

Where it's used

Why this math matters outside the classroom:

  • Road trips. A driver with 3.5 gallons left at 28 mpg works out 3.5 × 28 = 98 miles before the tank is empty.
  • Rental cars abroad. A traveler converts 10 liters at 6.5 L/100 km into 10 ÷ 6.5 × 100, about 154 km of range.
  • Classroom rate problems. Students multiply a quantity of fuel by a constant rate in miles per gallon to find a distance.
  • Remote areas. Drivers on long stretches without stations check that a trip fits within their range with a margin.
  • Small boats and generators. Owners estimate run time or distance from fuel left and a known fuel use rate.

Grade level and standards: Grade 6; Common Core State Standards for Mathematics 6.RP.A.3.b, 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Choose whether you know the gauge reading or the amount of fuel in the tank.
  2. Enter the tank size and gauge reading, or the fuel amount, with its unit.
  3. Enter your fuel economy and its unit. Keep or change the safety margin.
  4. Choose miles or kilometers. If you like, enter the distance still to drive. Then read the range.

What the inputs mean

Tank size
The usable capacity from the owner's manual or the maker's specifications. A fill-up from near empty shows roughly how much your tank takes in practice.
Gauge reading
Read it as a share of a full tank: a quarter is 25%, and an eighth is 12.5%. Fuel gauges often don't move evenly, and many read low near empty. So treat this as an estimate.
Fuel left in the tank
Use this if you know how much fuel is in the tank. For example, after you add a set amount to a nearly empty tank.
Fuel economy
Your real average, not the official figure. Divide the distance driven by the fuel used since the last fill-up, or read the trip computer. Steady highway driving usually does better than city traffic. Towing, heavy loads, roof boxes and cold weather do worse.
Safety margin (optional)
A percentage of the range kept in reserve. It allows for gauge error, detours, traffic and the time it takes to find a station.
Distance still to drive (optional)
The distance you still need to cover, in the unit chosen above.

Formula and method

fuel left = tank size × gauge reading
range = fuel left × miles per gallon (or km per liter)
range in km = liters left ÷ (L/100 km) × 100
safe range = range × (1 − safety margin)
fuel to add = fuel left × (trip − safe range) ÷ range

Range is how far the fuel will take you. Safe range is that distance minus your safety margin, and trip is the distance you still plan to drive. The fuel and the economy may use different volume units. If so, the fuel is converted first, using exact definitions. 1 US gallon is 3.785411784 liters, and 1 imperial gallon is 4.54609 liters. The range comes out in the economy's own distance unit. Then it's converted to miles or kilometers, with 1 mile = 1.609344 km.

L/100 km measures the fuel used over a distance, not the distance per unit of fuel. So the fuel is divided by it, then multiplied by 100. The fuel to add is the extra distance beyond the safe range, turned back into fuel at the same rate.

Worked example

Your car has a 14-gallon tank, the gauge shows a quarter, you average 28 mpg, and you want a 10% margin. The next town with a station is 95 miles away.

  1. Fuel left: 14 US gal × 25% = 3.5 US gal.
  2. Range: 3.5 × 28 = 98 miles (157.7 km).
  3. Keeping a 10% margin: 98 × (1 − 10%) = 88.2 miles.
  4. The 95-mile drive is 107.71% of the safe range, so it only fits by eating into the margin.
  5. Adding 3.5 × (95 − 88.2) ÷ 98 = 0.24 US gal would restore the margin.

Result: A quarter tank gives about 98 miles of range, or 88.2 miles with a 10% margin. So a 95-mile drive is cutting it close.

Understanding the result

Treat the range as an estimate, not a promise. The safe range is the number to plan with. The full range is closer to the absolute limit, and it leaves nothing for a detour or a closed station.

The result may say you can only make it by using your margin. If so, refuel at the first handy chance rather than counting on the last few miles. Running a tank very low can also be hard on some fuel pumps. And running out on a busy road is unsafe.

Comparing this figure with the car's distance-to-empty display is a good check. If they differ a lot, the car may be using a recent short-term average that doesn't match the road ahead.

Assumptions and limitations

  • The fuel economy you enter holds for the rest of the drive.
  • The gauge reading is a true share of the usable tank.
  • Unit conversions use exact definitions of the gallon and the mile.
  • Gauges are approximate and often uneven, especially near empty. Some fuel at the bottom of the tank may not be usable.
  • Hills, speed, wind, temperature, load and air conditioning all change fuel economy along the way.
  • This is a planning estimate. When in doubt, refuel early.

Frequently asked questions

How far can I drive when the fuel light comes on?

It depends on the vehicle. The light is set to come on with a certain amount of fuel left, and the owner's manual sometimes states it. Enter that amount and your fuel economy here for an estimate. Then plan to refuel well before reaching it.

Why does my car's distance-to-empty figure differ from this?

Cars estimate range from recent driving. After a stretch of city traffic or a fast highway run, that can be far from your long-run average. This calculator uses the economy you enter, so a realistic figure gives a steadier estimate.

How do I work out my real fuel economy?

Fill the tank, reset the trip meter and drive normally. Then fill up again. Divide the distance by the fuel it took to refill. The mpg calculator can convert the result between mpg, L/100 km and km/L.

Is it bad to drive on a nearly empty tank?

Running out is the main risk, and it can leave you stranded somewhere unsafe. In many vehicles, the fuel also helps cool the fuel pump. So running very low as a habit isn't recommended. A margin of a tenth of the range or more is a sensible habit.

How this calculator is checked

Method: Fuel left × distance per unit fuel; exact unit definitions (1 US gal = 3.785411784 L, 1 imperial gal = 4.54609 L, 1 mi = 1.609344 km). The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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