Cubic Metres: Volume Formula and Unit Conversion

A cubic metre measures three-dimensional space

A metre is a unit of length; a cubic metre, written m³, is a unit of volume. One cubic metre is the volume of a cube with sides each one metre long. Square metres measure area and cannot be converted to cubic metres without another length, such as thickness or depth. This distinction matters for tanks, soil, concrete and freight. An order for ten square metres of material is incomplete for a volume calculation until the intended thickness is specified. Keep the exponent visible whenever recording the unit.

Calculate a rectangular volume

For a rectangular container or solid, V=length×width×height. A box measuring 2 metres by 0.5 metre by 0.4 metre has volume 0.4 cubic metre. All dimensions must describe the same relevant boundary. For usable container capacity, internal dimensions are appropriate; external dimensions include the walls and can overstate capacity. If the container is filled only to a marked level, use that fluid height instead of the total exterior height. Geometry alone does not determine whether a container is structurally suitable for the contents.

Convert cubic metres and litres

One litre equals one cubic decimetre, and one cubic metre equals 1,000 litres. The 0.4-cubic-metre box therefore has a geometric volume of 400 litres. Conversely, 250 litres equals 0.25 cubic metre. A millilitre equals one cubic centimetre, so one cubic metre contains 1,000,000 millilitres. These are volume relationships, not assumptions about the substance. A 250-litre volume of air and a 250-litre volume of water occupy the same nominal space even though their masses differ substantially.

Cube the length-conversion factor

There are 100 centimetres in a metre, so there are 100³=1,000,000 cubic centimetres in a cubic metre. There are 1,000 millimetres in a metre, so there are 1,000³=1,000,000,000 cubic millimetres in a cubic metre. Dividing a cubic-centimetre number by 100 merely applies a length conversion and gives the wrong result. As an independent check, a cube with sides 100 centimetres has volume 100×100×100 cubic centimetres, which is exactly the same cube as the one-metre cube.

Compare cubic feet and identify gallon conventions

Using the exact foot of 0.3048 metre, one cubic foot equals 0.028316846592 cubic metre. Therefore one cubic metre is approximately 35.3147 cubic feet. For gallons, the convention matters: a US liquid gallon and an imperial gallon have different volumes. The linked volume converter's gal option uses a US liquid gallon, approximately 3.785411784 litres. Label it as US when reporting a result. The word gallon by itself may be ambiguous for a reader using a different regional system.

Convert volume to mass only with density

Mass equals density multiplied by volume, with compatible units. If a stated material density is 1,600 kilograms per cubic metre and its volume is 0.4 cubic metre, its calculated mass is 640 kilograms. This is an illustration of the relationship, not a universal density for soil or gravel. Moisture, compaction, temperature and material composition can alter density. A converter cannot infer those properties from volume alone. Use an appropriate measured or supplier-provided density and identify whether it refers to loose, compacted or solid material.

Verify the converter with a round trip

Select m3 as the source unit, l as the target, and enter 0.4 to obtain 400 litres. Reverse the units and enter 400 to recover 0.4 cubic metre. For an irregular shape, obtain its volume using an appropriate shape formula or measurement method before converting units. A round trip checks the unit factor; it does not validate an estimate of the original shape. Keep measured dimensions, internal-versus-external assumptions and the chosen unit convention with the result, especially when it will be used for purchasing or transport planning. Label litres as L in a written report to distinguish the unit from the numeral one.

Related guides

Can You Convert Length to Volume? Required Dimensions

Calculate volume when length is combined with a shape and cross-section, and learn why a length alone cannot determine cubic units or capacity.

Calculate Container Volume from Internal Dimensions

Estimate rectangular or cylindrical container capacity, convert cubic units to litres, and account for internal dimensions, headspace and partial filling.

Volume to Mass or Weight: Use Density and Units

Convert volume to mass using density, distinguish mass from weight force, and choose bulk density or material density to match the measured volume.