Fuel Tank Capacity Calculator
Pick a tank shape and fuel type to get capacity in gallons and liters, plus the liquid's approximate mass.
How it works
Each shape uses its own geometric volume formula (rectangular: L×W×H; vertical cylinder: π×r²×H; horizontal cylinder: π×r²×L), converted from cubic inches to US gallons by dividing by 231. Mass multiplies the volume in liters by the selected fuel's typical density. The "approximate usable" figure assumes about 5% vapor space (ullage), a common allowance so tanks aren't filled to the geometric brim.
Worked example
A horizontal cylindrical tank 24 in diameter × 48 in long holds π × 12² × 48 ÷ 231 ≈ 94 gallons geometrically. At 95% usable, that's about 89.3 gallons. Filled with gasoline (≈0.74 kg/L), the full tank's liquid mass is roughly 94 × 3.785 × 0.74 ≈ 263 kg (≈580 lb).
Assumptions
- Tank walls are thin enough that inside dimensions ≈ outside dimensions.
- Fuel densities are typical values at normal ambient temperature; actual density varies with fuel blend and temperature.
- The 95% usable allowance is a common rule of thumb, not a specific code requirement for your tank.
Reference
Flammable and combustible liquid storage is governed by NFPA 30, Flammable and Combustible Liquids Code. Consult a qualified professional for any fuel storage installation.
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Frequently asked questions
How do I calculate fuel tank dimensions to capacity?
Compute geometric volume from the tank's shape, convert to gallons by dividing by 231, and multiply by fuel density for mass.
Can a fuel tank actually be filled to its full rated capacity?
Usually not quite — tanks commonly keep some vapor space (ullage) for thermal expansion and safety, so usable capacity is slightly below the geometric total.
Is this calculator safe to use for fuel storage design?
No — it only estimates volume and mass. Fuel storage design is governed by codes like NFPA 30 and needs a qualified professional.