One cubic metre is exactly 1,000 litres. The thousand comes from the cube of ten: a cubic metre is a thousand cubic decimetres, and a litre is defined as exactly one cubic decimetre.
About the units
The cubic metre is the SI unit of volume and the litre is an accepted non-SI unit defined in terms of it. The relationship is the clearest example of why cubing catches people out: a metre is ten decimetres, and 10³ is 1,000, so the volume factor is a thousand where the length factor was ten. The same logic runs one step further down — a cubic metre is 1,000,000 cubic centimetres, since a metre is a hundred centimetres and 100³ is a million. Anyone who has internalised the squaring rule for areas needs the cubing rule too, and the errors it prevents are larger.
The exact factor
The factor is exactly 1,000. A useful physical anchor: one cubic metre of fresh water weighs one tonne, because a litre of water weighs a kilogram and there are a thousand litres in the cubic metre. That coincidence is not a coincidence — it is what the metric system was designed to produce, and it makes hydraulic and structural calculations unusually easy. A 1,000-litre intermediate bulk container, the standard white cube on a pallet, holds exactly one cubic metre.
Where you meet this conversion
Water and gas billing, where consumption is metered in cubic metres and appliance capacities are stated in litres. Construction uses cubic metres for concrete, excavation and fill while material data sheets give litres per bag. Shipping and freight quote volumes in cubic metres. Aquariums, tanks and rainwater harvesting all cross the boundary: a tank described as 5 m³ holds 5,000 litres, and the two figures appear on the same specification sheet.