Tank volume calculator
Capacity of a rectangular, cylindrical or capsule-shaped tank, in litres, US gallons and cubic units.
Formula and worked example
Rectangular box: V = l × w × h
Cylinder: V = π r² h
Capsule: V = πr²a + (4/3)πr³
Example: a rectangular box with l = 5 cm, w = 3 cm, h = 2 cm holds 30 cm³ = 0.03 litres.
Fish tanks and water troughs are usually rectangular; water heaters and rain barrels are cylinders; propane and fuel tanks are often capsules (a cylinder with rounded ends).
Other solids
Need the outside area for paint or material instead? Use the surface area calculator.
Questions people ask
How do I calculate the capacity of a water tank?
Pick the tank shape, measure its inside dimensions in one unit, and read the litres or gallons. Use inside measurements: wall thickness can make a noticeable difference on small tanks.
How many gallons is a 48 × 12 × 20 inch aquarium?
48 × 12 × 20 = 11,520 in³, and 11,520 ÷ 231 ≈ 49.9 US gallons when filled to the brim.
How do I measure a capsule (propane) tank?
Enter the radius of the round cross-section and the length of the straight cylindrical part only, not the overall length including the domed ends.