Fuel tank capacity calculator
How many gallons and liters a rectangular or cylindrical fuel tank holds from its inside dimensions, and how much is usable at your fill level.
Your numbers
Rectangular tankCylindrical tankUse See your resultResult
Rectangular tank 99.7 gal378 L; 89.8 gal usable Cylindrical tank 65.3 gal247 L; 58.8 gal usable Stop working this out by handFleetZap fuel logs record gallons and cost for every unit, so you can see what each one burns between fill-ups.
See FleetZap Maintenance · Try the demoThe formula
Gallons = Volume in cubic inches ÷ 231 · Rectangle = L × W × H · Cylinder = π ÷ 4 × Diameter² × Length
A US gallon is 231 cubic inches. With the example: 48 × 24 × 20 in is 99.7 gallons, and a 20 in by 48 in cylinder holds 65.3. Measure inside dimensions; wall thickness, baffles and rounded corners make real tanks hold a little less. Leave any blank group at 0.
Using the numberWhat to do with it
- Run time on a tank = usable gallons ÷ fuel burned per hour; the generator fuel calculator works out the burn.
- Mark the tank’s real capacity on it, so fill-ups and fuel logs can be checked against it.
- A tank that takes more than it holds at a fill-up points at a leak, a theft or a wrong reading.
Guides behind this calculator
Fuel truck maintenance Fleet fuel management Generator maintenanceMore free calculators
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Good to know
How do you calculate fuel tank capacity?Find the volume in cubic inches and divide by 231. A rectangular tank is length × width × height; a cylinder is π ÷ 4 × diameter² × length.
How many liters is a gallon?One US gallon is about 3.785 liters.
Why does my tank hold less than calculated?Wall thickness, baffles, fittings and rounded corners take up space, and tanks shouldn't be filled to the brim.
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