Cubic Feet, Cubic Yards and Cubic Metres: Converting Job Volumes
A single building job can use four different volume units. Bags of concrete or compost state their contents in cubic feet, a delivery driver talks in cubic yards or cubic metres, a pond liner comes with a size in litres or gallons, and the depth you measured is in inches or millimetres. Mistakes at the unit stage are the most common reason a quantity comes out ten times too big or too small.
This guide collects the conversions you need, explains why area and volume factors are squares and cubes of the length factor, and runs one example through all the units so you can see the pattern.
The conversions that matter
| Quantity | Equals |
|---|---|
| 1 cubic yard | 27 cubic feet = 0.7646 cubic metres |
| 1 cubic metre | 35.31 cubic feet = 1.308 cubic yards = 1,000 litres |
| 1 cubic foot | 28.32 litres = 7.48 US gallons |
| 1 US gallon | 3.785 litres (a UK gallon is 4.546 litres) |
| 1 inch | 25.4 millimetres (exactly) |
| 1 foot | 0.3048 metres (exactly) |
For quick mental estimates, remember that one cubic metre is about 1.3 cubic yards, and one cubic yard is about three-quarters of a cubic metre (0.76). The table holds the more precise values for ordering.
Why area and volume factors are not the length factor
A yard is 3 feet, but a square yard is not 3 square feet. It is a 3 ft by 3 ft square, which holds 9 ft². A cubic yard is a 3 × 3 × 3 ft block, which holds 27 ft³. The same rule applies to every unit pair: square the length ratio for area and cube it for volume.
area factor = (length factor)² volume factor = (length factor)³A metre is 3.281 ft, so a square metre is 10.76 ft² and a cubic metre is 35.31 ft³.
Forgetting this is a classic error. Someone who knows 1 m = 3.28 ft and applies it to a volume will understate the answer drastically. When in doubt, convert the lengths first, then multiply them, and the right factor appears automatically.
One slab, four units
A concrete pad is 12 ft by 15 ft and 4 in thick. The wrong way is to multiply 12 × 15 × 4 and get 720, which is neither cubic feet nor anything else useful. The right way is to put the depth in feet first.
- Thickness: 4 in ÷ 12 = 0.333 ft.
- Volume: 12 × 15 × 0.333 = 60 ft³.
- Cubic yards: 60 ÷ 27 = 2.22 yd³.
- Cubic metres: 60 × 0.02832 = 1.70 m³, which is about 1,699 litres.
Bagged materials follow the same path. Twenty-five bags of mulch at 2 ft³ each make 50 ft³, which is 50 ÷ 27 = 1.85 yd³, or 50 × 0.02832 = 1.42 m³. A water butt or tank is the same idea in other units: 200 US gallons is 200 × 3.785 = 757 litres, or 200 × 0.1337 = 26.7 ft³.
Going the other way, if a supplier quotes a 3 m³ load, you divide by 0.7646 to get 3.92 yd³, or multiply by 35.31 to get 105.9 ft³. Use the volume converter for these, the length converter for dimensions, and the area unit converter when your plan is in square feet but a supplier works in square metres.
Weights and gallons
Some materials are sold by weight, and three different "tons" are in use. A US short ton is 2,000 lb (about 907 kg). A metric tonne is 1,000 kg (about 2,205 lb). A UK long ton is 2,240 lb (about 1,016 kg). Check which one a quote means.
Gallons also differ. A US gallon is 3.785 litres and an imperial (UK) gallon is 4.546 litres, about 20% larger. This matters when you compare the capacity of a water tank, a pond or a paint can from different countries.
- Convert every dimension to one unit before multiplying anything.
- Keep full precision in the middle of a calculation and round only the final answer.
- Round up when the result is a number of bags, boxes or loads.
- Sanity-check the result: a typical garden bed should be a few cubic yards at most, not hundreds.
Once the volume is in the right unit, you can move on to quantity: see our guides to concrete and to mulch, gravel and topsoil.
- Volume Converter: Pick a number and two units to convert between 25 metric, US and imperial volume units, from cubic kilometers down to teaspoons. The answer updates as you type.
- Length Converter: Pick a unit, type a length, choose the unit you want and read the answer. The converter covers metric, imperial and nautical units in one place.
- Area Converter: Pick a unit on each side, type an area and the converted value appears straight away. The guide lists the exact size of every unit in square meters, with worked examples and the mistakes to avoid.
This article is general information, not professional advice. See our Disclaimer and Editorial Policy.
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