Room Volume Calculator
The volume of a room or box, in cubic metres, feet and litres.
Good to know. A 4 × 4 m room with a 2.5 m ceiling holds 40 m³ of air, and one argument about the thermostat.
How it works
In plain words
Multiply the length, width and height. All three must be in the same unit. One cubic metre holds 1,000 litres.
The formula
V = length × width × height 1 m³ = 1,000 L = 35.3147 ft³
Worked example
A room 5 × 4 m with a 2.5 m ceiling holds 5 × 4 × 2.5 = 50 m³ of air, which is 50,000 litres or about 1,765.73 ft³.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B Exact conversion factors for US customary units.
- International yard and pound agreement, 1959 1 yard = 0.9144 m and 1 pound = 0.45359237 kg exactly, so 1 inch = 2.54 cm and 1 mile = 1.609344 km.
Sources checked September 29, 2026. 4 automated tests check its answers on every change.
About the room volume calculator
Room volume is the amount of space inside a room, and it is what matters for heating, cooling, ventilation, air purifiers and dehumidifiers. Manufacturers often rate these by the room volume they can handle, or by how many times an hour they can replace or clean the air in it.
For a rectangular room or box, multiply length × width × height. Make sure all three measurements use the same unit. If your room has a sloping ceiling, use the average height; if it is L-shaped, split it into rectangles and add the volumes.
A useful example is air changes per hour. If a bathroom extractor fan moves 90 m³ an hour and the bathroom is 15 m³, it changes the air 6 times an hour. Building guidance commonly asks for more in kitchens and bathrooms than in living rooms.
The same calculation works for moving boxes, storage units, raised garden beds, aquariums and water tanks. For containers, one cubic metre is 1,000 litres, and one litre is a 10 × 10 × 10 cm cube, so a tank measured in centimetres converts easily: divide cubic centimetres by 1,000 for litres.
Questions people ask
How do I calculate the volume of a room?
Multiply the length, width and height. A 5 × 4 m room with a 2.5 m ceiling is 50 m³.
How many litres are in a cubic metre?
1,000 litres.
How do I convert cubic metres to cubic feet?
Multiply by 35.3147. 50 m³ is about 1,766 ft³.