The Volume Formulas
Example — a fish tank 2 ft × 1 ft × 1.5 ft
Volume = 2 × 1 × 1.5 = 3 ft³. Water is sold and dosed by the gallon: 3 × 7.481 = 22.4 US gallons — the size on the box at the pet store. For one-off conversions like that ft³-to-gallons hop, the unit converter does the same job. Three lengths multiplied, then converted: that is every volume problem.
Liters, Gallons and Cubic Feet: Which Unit When?
Match the unit to the job:
| Unit | Equals | Used for |
|---|---|---|
| Liter (L) | 1,000 cm³ | Tanks, engines, liquids (metric) |
| Cubic meter (m³) | 1,000 L | Pools, concrete, freight |
| Cubic foot (ft³) | 7.481 US gal | Appliances, soil, mulch (US) |
| US gallon | 3.785 L | Fuel, aquariums, paint (US) |
| Imperial gallon | 4.546 L | UK/Canada legacy — 20% bigger than US |
The US vs imperial gallon gap is the classic trap: a "30-gallon" tank means 114 L in Ohio and 136 L in Ontario. And remember where volume starts: multiply a cross-section from the area calculator by the depth and you have most real-world volumes.
How Much Does It Hold? Tanks, Pools and Boxes
Three runs people actually do:
- Pool: a round pool 4 m across and 1.2 m deep is a cylinder: π × 2² × 1.2 = 15.1 m³ = 15,080 liters of water (and chemicals dosed per 1,000 L).
- Moving boxes: a 60 × 40 × 40 cm box = 0.096 m³. A 10 m³ truck fits roughly 100 of them — before reality intervenes.
- Concrete: a slab is a flat box: 5 × 4 × 0.1 m = 2 m³ — the number the mixer truck charges you for.
For a container, always measure the inside dimensions (the tape measure calculator keeps the fractions honest) — wall thickness steals more than people expect.
Common Volume Mistakes
- Diameter instead of radius in cylinders and spheres — the error cubes: 2× the radius is 8× the volume — a scientific calculator shows how fast those powers grow.
- Forgetting the ⅓ in cones and pyramids — they hold exactly a third of their enclosing cylinder/box.
- Converting with a length factor: 1 m = 3.28 ft, but 1 m³ = 35.3 ft³ — cube the factor.
- US vs imperial gallons — a 20% difference hiding in one word.
- Outside dimensions for tanks and boxes (see above).
The Bottom Line
Volume is three lengths multiplied — with π where the solid curves and a ⅓ where it tapers to a point. Pick the solid above, measure in one consistent unit, and read the answer in liters, gallons or cubic meters as your project needs. Comparing two tank sizes? The percentage calculator turns the difference into a percent.