Cubic Units Explained
The one rule to remember: when you convert a cubic unit, you cube the length factor. Feet to inches is × 12, so cubic feet to cubic inches is × 12³ = 1,728. That single idea explains every conversion on this page — why a cubic yard is 27 cubic feet, and a cubic metre is a million cubic centimetres.
What a cubic unit is
A cubic unit is the space inside a cube one unit on each side. A cubic centimetre (cm³) is a cube 1 cm × 1 cm × 1 cm. A cubic foot (ft³) is a cube one foot on every edge. Because you are multiplying three lengths, the units multiply too: cm × cm × cm = cm³. That little "3" is not decoration — it is the reason cubic conversions behave so differently from ordinary length conversions.
Always cube the factor
Here is the trap that catches everyone. There are 3 feet in a yard, so it feels like there should be 3 cubic feet in a cubic yard. There are not — there are 27. A cubic yard is a cube 3 ft on every side, so it holds 3 × 3 × 3 = 27 cubic feet.
then 1 cubic big unit = k³ cubic small units
- 1 foot = 12 inches → 1 ft³ = 12³ = 1,728 in³
- 1 yard = 3 feet → 1 yd³ = 3³ = 27 ft³
- 1 metre = 100 cm → 1 m³ = 100³ = 1,000,000 cm³
Metric cubic units
| Unit | In cm³ | In litres |
|---|---|---|
| 1 cubic millimetre (mm³) | 0.001 | 0.000001 L |
| 1 cubic centimetre (cm³ = mL) | 1 | 0.001 L |
| 1 litre (L) | 1,000 | 1 L |
| 1 cubic metre (m³) | 1,000,000 | 1,000 L |
The neat part of the metric system: a cubic centimetre is a millilitre, and a cubic metre is a thousand litres, with no messy conversion factors. That is why lab and medical work — see the dilution calculator — lives comfortably in cm³ and mL.
Imperial & US cubic units
| Unit | In cubic inches | In US gallons |
|---|---|---|
| 1 cubic inch (in³) | 1 | 0.004329 gal |
| 1 cubic foot (ft³) | 1,728 | 7.4805 gal |
| 1 cubic yard (yd³) | 46,656 | 201.97 gal |
| 1 US gallon | 231 | 1 gal |
The US gallon is defined as exactly 231 cubic inches, which is where the 7.48 gallons-per-cubic-foot figure comes from (1,728 ÷ 231). Builders lean on the cubic yard — see the cubic yard calculator — because concrete and aggregate are sold that way.
Crossing between metric and imperial
- 1 cubic inch = 16.387 cm³ (= 16.387 mL)
- 1 cubic foot = 28.317 litres
- 1 cubic metre = 35.315 cubic feet
- 1 cubic yard = 0.7646 cubic metres
You never have to memorise these — the volume conversion calculator handles all of them, including liquid units. But knowing that the factor is always cubed lets you sanity-check any answer.
Frequently asked questions
How many cubic feet are in a cubic yard?
27. A yard is 3 feet, and 3 × 3 × 3 = 27, so one cubic yard contains 27 cubic feet.
Why is a cubic metre 1,000 litres?
A metre is 100 centimetres, so a cubic metre is 100 × 100 × 100 = 1,000,000 cubic centimetres. Since one litre is 1,000 cubic centimetres, that is 1,000 litres.
Is a cubic centimetre the same as a millilitre?
Yes, exactly. One cubic centimetre equals one millilitre by definition, which is why medical syringes are marked in both cc and mL.
How do you convert between cubic units?
Cube the length conversion factor. To go from feet to inches you multiply by 12, so to go from cubic feet to cubic inches you multiply by 12³ = 1,728.