Volume of a Cylinder Calculator
Enter the radius and height, pick a unit, and get the cylinder’s volume instantly — in cubic units plus gallons or liters, with the πr²h math shown step by step.
Example: with Radius (r) 3 · Height (h) 8 · Units feet (ft) → Volume: 226.19 ft³.
Computed by the calculator below using its default values. Change any input to see your own numbers.
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Check it outCylinder volume formula: V = πr²h
To find the volume of a cylinder, square the radius, multiply by π, then multiply by the height: V = πr²h. With the defaults above — a tank with a 3 ft radius and 8 ft height — that’s π × 3² × 8 = 72π ≈ 226.19 cubic feet, which holds about 1,692 gallons of water (1 ft³ = 7.48052 gal).
Most real-world measurements give you the diameter, not the radius — halve it first. A bucket 12 inches across and 24 inches tall has r = 6 in, so V = π × 36 × 24 ≈ 2,714.34 in³, or about 11.75 gallons (231 in³ per gallon). Whatever length unit you enter, the volume comes out in that same unit cubed.
How it’s calculated
Volume = π × r² × h, computed with full double-precision π. The base area row is πr². Conversions: 1 US gallon = 231 in³ exactly and 1 ft³ = 7.48052 gal (NIST Handbook 44); 1 liter = 1,000 cm³; 1 m³ = 1,000 L. Volume is reported in the cube of the unit you select.
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Entering the diameter as the radius — halve the diameter first, or the result comes out 4× too big.
- Mixing units, like a radius in inches with a height in feet — convert everything to one unit before you start.
- Rounding π to 3 — that alone skews the answer by about 4.5%; the calculator carries full precision.
Frequently asked questions
What is the cylinder volume formula?
V = πr²h — the base area (πr²) times the height. For r = 3 ft and h = 8 ft, V = π × 9 × 8 ≈ 226.19 ft³.
How do I find the volume of a cylinder from the diameter?
Divide the diameter by 2 to get the radius, then apply πr²h. A cylinder 10 inches across and 12 inches tall has r = 5, so V = π × 25 × 12 ≈ 942.48 in³ — about 4.08 gallons.
How many gallons does my cylinder hold?
Compute the volume in cubic feet and multiply by 7.48052, or compute it in cubic inches and divide by 231. This calculator shows the gallon (or liter) conversion automatically.
What units should I use?
Any single unit for both inputs — inches, feet, centimeters, or meters. The volume comes out in that unit cubed (in³, ft³, cm³, or m³).