Concrete in cubic metres, litres and cubic yards

By Kyle Bell · Reviewed November 9, 2026

Concrete quantities can be expressed in cubic metres, litres, cubic feet, or cubic yards. These are all volume units, but the measurements used to calculate them must be consistent. A common metric input combines length and width in metres with thickness in millimetres; the thickness needs conversion before the multiplication.

Calculate a metric slab directly

For a supplied design measuring 3 metres long, 2 metres wide, and 100 millimetres thick, convert the thickness to 0.1 metre. Volume is 3 × 2 × 0.1 = 0.6 cubic metre. The same amount is 600 litres because one cubic metre contains 1,000 litres.

A selected 5% allowance raises the requirement to 0.63 cubic metre, or 630 litres. If the chosen product states a yield of 20 litres per bag, divide 630 by 20 to obtain 31.5 bags, rounded up to 32. The nominal available volume is 640 litres, with 10 litres of package surplus beyond the selected allowance.

Distinguish a kilogram bag from a litre yield

A bag labelled 20 kilograms does not automatically yield 20 litres of concrete. Kilograms describe mass, while litres describe volume. The 20-litre figure in this worked example is a hypothetical stated yield, not a rule for bags of any particular weight.

Look up the actual product's instructions or technical sheet. The QUIKRETE No.1101 sheet, for instance, provides both package mass and approximate mixed volume. Keep the yield input editable because formulations and package sizes differ across products and markets.

Convert the calculated volume only when needed

One cubic foot is 0.028316846592 cubic metre, and one cubic yard is 0.764554857984 cubic metre. These exact relationships follow from the international foot and yard definitions; NIST's tables provide the conversion reference, with some displayed factors rounded.

The 0.6-cubic-metre example is therefore approximately 21.189 cubic feet or 0.785 cubic yard. Its 5%-adjusted 0.63 cubic metre is approximately 0.824 cubic yard. Conversion alone does not apply an allowance or round a supplier's order. Those remain separate steps.

Check mixed-unit entries carefully

A thickness of 100 millimetres equals 10 centimetres and 0.1 metre. Entering 100 into a centimetre field would multiply the required volume by ten. A clear input label is more valuable than showing many decimal places in the answer. If a tool changes unit mode, verify that it converts the stored dimensions instead of merely relabelling the same numbers.

When dimensions arrive from different drawings, convert each measurement before combining them. Record which plan or measurement supplied the dimensions, particularly where a depth changes across the pour. Do not treat the calculator's example dimensions as recommendations for structural use.

Save the measured volume in its original unit and include the converted supplier quantity alongside it. For purchasing, use the chosen product's yield or the supplier's confirmed order increment. Preserve full precision until the final rounding step so an intermediate conversion does not accidentally add or remove a bag.

Sources & further reading

• NIST Guide to SI, Appendix B.8 — Conversion factors
• QUIKRETE Concrete Mix No.1101 — Technical data sheet

Source material checked November 9, 2026. This guide is an original explanation; source publishers do not endorse this website.