Cylinder Cubic Feet Calculator

How to calculate the cubic feet of a cylinder

A cylinder is a 3D shape made by stacking identical circular discs. The volume is the area of one circle (π × r²) multiplied by the height the discs are stacked (H). All you need are two measurements: the radius and the height, both in feet.

Worked examples

Example 1: A 4-foot-diameter water tank, 6 feet tall

Radius = 4 ÷ 2 = 2 ft. Volume = π × 4 × 6 ≈ 75.4 ft³, or about 564 US gallons.

Example 2: A concrete sonotube footing, 12-inch diameter, 4 feet deep

Radius = 6 in = 0.5 ft. Height = 4 ft. Volume = π × 0.25 × 4 ≈ 3.14 ft³, or about 0.12 cubic yards. That's about 5 of the standard 80 lb concrete bags per footing.

Example 3: A round planter, 18 inches across, 14 inches tall

Radius = 9 in = 0.75 ft. Height = 14 in = 1.167 ft. Volume = π × 0.5625 × 1.167 ≈ 2.06 ft³ of soil capacity — a little more than one standard 2 ft³ bag.

Example 4: A grain silo, 12 ft diameter × 30 ft tall

Radius = 6 ft. Volume = π × 36 × 30 ≈ 3,393 ft³, or about 25,377 US gallons of dry capacity.

Calculating in inches or other units

If your radius and height are in inches, the cleanest method is to convert each to feet first (divide by 12), then apply π × r² × H. Alternatively, compute the volume in cubic inches first and divide by 1,728 to convert to cubic feet.

Common uses for the cylinder calculator

• Cylindrical concrete footings (sonotube), pillars, and columns
• Round water tanks, oil drums, and storage cylinders
• Round planters, ceramic pots, and tree wells
• Pipes, conduits, and culverts
• Silos and grain bins
• Round above-ground swimming pools and hot tubs

Common mistakes to avoid

1. Using diameter instead of radius. The formula needs radius squared, not diameter squared. Using diameter directly gives 4× the correct volume.
2. Forgetting to square the radius. The formula is r², not r. Skipping the square gives a result that's far too small.
3. Using outer dimensions for an inner volume. Tanks have walls — for capacity, use the inside radius.
4. Mixing units between r and H. Both must be in feet (or both in inches with the result divided by 1,728).

Expert tips

1. Use radius, not diameter. The most common cylinder error is plugging diameter into the formula. Radius is half the diameter — measure across, divide by two.
2. Watch the height units. A cylinder formula has radius squared, so a unit error on radius gets squared too. If radius is in inches and height is in feet, your answer is wrong by 12² = 144 — not 12.
3. For pipes, measure the inside. Pipe outer diameter (OD) and inner diameter (ID) differ by twice the wall thickness. For volume of liquid the pipe can hold, use ID.
4. Sanity-check against gallons. 1 ft³ = 7.48 gallons. A 55-gallon drum is about 7.4 ft³ — if you get 70 ft³ for a 55-gallon drum, you forgot a unit conversion. See the cubic feet to gallonsconverter.
5. Use the cylinder calculator for round pools and tanks. Round above-ground pools, water tanks, and silos all follow πr²h. The pool calculator and water calculator apply this for specific applications.