Volume Calculator
Pick a shape, enter its dimensions in your unit, and get the volume — plus the capacity in liters and US gallons, which is what you actually need for tanks, planters and aquariums. The formula used is shown step by step.
Volume formulas
Each solid has its own formula, but they're related: a cone is exactly one third of the cylinder around it, and a sphere is two thirds of the cylinder it fits in (Archimedes' favorite theorem):
To turn volume into capacity, convert to a liquid unit: 1 cubic foot ≈ 28.32 L ≈ 7.48 US gallons; 1,000 cm³ = 1 L. The calculator does this for whatever unit you chose.
Worked examples
Example 1: aquarium capacity
A 24 × 12 × 16 inch aquarium — how many gallons?
- Volume in cubic inches.24 × 12 × 16 = 4,608 in³
- A US gallon is 231 in³.4,608 ÷ 231 = 19.9 gal
About 20 gallons — the standard "20 gallon high" tank size.
Example 2: cylindrical rain barrel
A barrel 2 ft across and 3 ft tall — how much water?
- Radius is half the diameter.r = 1 ft
- Cylinder volume.π × 1² × 3 = 9.42 ft³
- Convert to gallons.9.42 × 7.48 = 70.5 gal
About 70 US gallons (267 liters).
Example 3: cone of sand
A dumped sand pile ≈ a cone 6 ft wide, 2 ft tall. Volume?
- Radius 3 ft; cone = cylinder ÷ 3.π × 3² × 2 ÷ 3 = 18.85 ft³
- Sanity check in cubic yards for ordering.18.85 ÷ 27 ≈ 0.7 yd³
About 0.7 cubic yards of sand.
FAQ
What's the difference between volume and capacity?+
Volume is the space a solid occupies (cubic units); capacity is how much liquid it holds (liters, gallons). Numerically they match for a hollow container with thin walls — that's why the calculator shows both.
How many liters in a cubic meter, and gallons in a cubic foot?+
1 m³ = 1,000 L. 1 ft³ ≈ 28.32 L ≈ 7.48 US gallons. 1 US gallon is exactly 231 cubic inches.
I measured the diameter — what do I enter as radius?+
Half of it. Entering the diameter where a radius belongs inflates a cylinder's volume 4× and a sphere's 8× — the most common volume mistake.
Which shapes are coming next?+
Rectangular and cylindrical tanks cover most everyday needs; planned additions are cube, capsule (pill tank), pyramid and truncated cone (bucket).
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