Tank Volume Calculator
Tank capacity is the inside volume: π × (diameter ÷ 2)² × height for a vertical cylinder, the same with length for a horizontal one, and length × width × height for a rectangular tank. A vertical tank 48 in across and 6 ft tall holds 75.4 ft³ — about 564 US gallons. For pipework, use the Pipe Volume Calculator.
How it's calculated: Cylinder: V = π × (diameter ÷ 2)² × height or length; rectangle: V = L × W × H; 1 ft³ ≈ 7.48 US gallons.
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
Vertical cylinder: V = π (d/2)² h Horizontal cylinder: V = π (d/2)² L
Rectangular: V = L × W × H Oval: V = (π (w/2)² + w·(H−w)) × L
Horizontal cylinder partial fill uses the circular-segment area A = r²(θ − sin θ)/2
Run the calculation to see each step with your own numbers.
A vertical cylinder tank, 48 in diameter, 6 ft tall, full.
V = π × (2 ft)² × 6 ft = 75.4 ft³
≈ 564 US gallons
- Straight-walled tank with flat ends. Dished, hemispherical or coned ends hold slightly more or less — not modelled here.
- Partial-fill volume is available for vertical cylinders, horizontal cylinders and rectangular tanks; an oval tank reports full capacity only.
- Wall thickness is ignored — dimensions are treated as the inside of the tank.
- My horizontal tank is half full — why isn't that half the gallons?
- It is, exactly — a horizontal cylinder is symmetric top-to-bottom. But at any other level the relationship is curved: a tank filled to ¼ of its diameter holds less than ¼ of its capacity. The calculator handles that.
- Which shape is my tank?
- A standing round tank is a vertical cylinder; a tank lying on its side is a horizontal cylinder; a rectangular box tank is 'rectangular'; a tank with a flattened round cross-section (common for heating oil) is 'oval'.
- Does wall thickness matter?
- For most tanks, no — the calculator treats your dimensions as the inside of the tank, and a thin wall changes the capacity by a fraction of a percent. Measure the internal size if the walls are thick.
- How many gallons are in a cylindrical tank?
- Multiply π by the radius squared and by the height (vertical) or length (horizontal), then convert: 1 ft³ ≈ 7.48 US gallons. A 48 in diameter tank 6 ft tall holds 75.4 ft³, about 564 gallons.
- How do you work out the volume of a partly filled horizontal tank?
- The liquid fills a circular segment of the tank end, with area r²(θ − sin θ)/2, multiplied by the tank length. Enter the fill depth from the bottom and the calculator does this; at half full it is exactly half the capacity.
Geometry
Standard geometry; the circular-segment area for a partly full horizontal cylinder is A = r²(θ − sin θ)/2. Unit conversions per NIST SP 811.
About the Tank Volume Calculator
The Tank Volume Calculator gives a tank's full capacity and its volume at a chosen fill depth, for a vertical or horizontal cylinder, a rectangular tank, or a horizontal oval. The partial-fill maths matters most for a horizontal cylinder, where the volume at a given depth follows a curve rather than a straight line. Dimensions are treated as the inside of the tank.
What you enter
- Tank shape
- Diameter
- Height
- Diameter
- Length
- Length
- Width
- Height
- Width (minor axis)
- Height (major axis)
- Length
- Fill depth — Leave 0 for the full capacity. For a horizontal cylinder, measured from the bottom.
What you get back
- Full capacity — the exact result of the calculation.
- Volume at fill depth — Shown only when you enter a fill depth.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Pipe Volume Calculator — Volume of liquid a length of pipe holds from its diameter and length.
- Pond Calculator — Volume of a pond and the liner size it needs.
- Cubic Yard Calculator — Convert a length, width and depth into cubic yards, cubic feet or cubic metres.
Part of the Water & Volume calculators.