Concrete mix calculator: cement, sand and gravel
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| Concrete needed | 1 m³ |
| Mix | 1 : 2 : 4 cement, sand, gravel |
| Parts sharp sand | 2 parts |
| Parts gravel | 4 parts |
| Waste allowance | 0% |
| Dry-volume factor | 1.54 × |
| Cement density | 1,440 kg/m³ |
| Sharp sand density | 1.6 t/m³ |
| Gravel density | 1.6 t/m³ |
| Cement bag size | 25 kg |
| Bulk bag size | 0.85 t |
Order: 13 × cement bags, 0.70 t sharp sand and 1.41 t gravel
| Result | Value |
|---|---|
| Cement bags | 13 |
| Cement | 316.8 kg |
| Sharp sand | 704 kg |
| Sharp sand bulk bags | 1 |
| Gravel | 1.41 t |
| Gravel bulk bags | 2 |
| Or order ready-mix (wet volume, with waste) | 1 m³ |
| Part | Parts | Dry volume |
|---|---|---|
| Cement | 1 | 0.22 m³ |
| Sharp sand | 2 | 0.44 m³ |
| Gravel | 4 | 0.88 m³ |
Show the working
- Wet concrete: 1 m³ × 1 (0% waste) = 1 m³
- Dry materials: 1 × 1.54 = 1.54 m³
- Mix 1 : 2 : 4, so 7 parts in all
- Cement: 1.54 ÷ 7 = 0.22 m³ × 1,440 kg/m³ = 316.8 kg
- Sharp sand: 1.54 × 2 ÷ 7 = 0.44 m³ × 1.6 t/m³ = 0.7 t
- Gravel: 1.54 × 4 ÷ 7 = 0.88 m³ × 1.6 t/m³ = 1.41 t
- Bulk bags: tonnes ÷ 0.85 t, rounded up (sharp sand 1, gravel 2)
- Cement bags: 316.8 kg ÷ 25 kg, rounded up = 13
How it works
- Wet volume = concrete needed × (1 + waste); dry volume = wet × dry-volume factor
- For a 1 : s : g mix, total parts P = 1 + s + g (or 1 + r for 1 : r all-in ballast)
- Cement (m³) = dry ÷ P; cement (kg) = cement m³ × cement density; bags = kg ÷ bag size, rounded up
- Sand (m³) = dry × s ÷ P; gravel (m³) = dry × g ÷ P; tonnes = m³ × density
- Water = cement bags × the maker's litres per bag (low to high)
Mix ratios are typical mixes quoted by cement makers, not strength classes. For footings or anything structural, follow the engineer's or cement maker's specification.
Ready-mix: ask your supplier about minimum loads.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Parts all-in ballast: 1 : 5 cement to all-in ballast | 5 parts ballast to 1 cement | Our assumption Not yet checked against the source | Our choice: change it to suit your job A mix quoted by cement makers for general concrete (brief v2 G1). Check the cement maker’s or engineer’s spec; this is not a strength class. |
| Waste allowance | 5 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job Uneven ground and spillage. |
| Dry-volume factor | 1.54 × | Our assumption Not yet checked against the source | Our choice: change it to suit your job Dry materials shrink when water is added (brief v2 G1). Researcher to check against Hanson, Tarmac or Blue Circle mixing guidance. |
| Cement density | 1440 kg/m3 | Our assumption Not yet checked against the source | Our choice: change it to suit your job Typical planning figure with no source yet. Researcher to source it and reclassify as typical. |
| Sharp sand density | 1.6 t/m3 Sources range 1.6–1.7 t/m3 | Typical value Not yet checked against the source | aggregatecalculator.co.uk aggregate density table (checked 19 October 2026) Damp sand bulks; order by weight. |
| Gravel density | 1.6 t/m3 Sources range 1.6–1.75 t/m3 | Typical value Not yet checked against the source | agg.directory calculator; aggregatecalculator.co.uk density table (checked 19 October 2026) Gravel and pea shingle. Sources differ, so the range is shown. |
| Ballast density | 1.8 t/m3 Sources range 1.7–1.9 t/m3 | Typical value Not yet checked against the source | aggregatecalculator.co.uk aggregate density table (checked 19 October 2026) |
| Cement bag size | 25 kg | Common UK size Not yet checked against the source | From your product Common UK cement bag. |
| Bulk bag size | 0.85 t | Common UK size Not yet checked against the source | builder.tools bulk bag figure (checked 19 October 2026) Varies by merchant; check yours. |
Regulations and standards
- BS 8500 (concrete): mix ratios here are not strength classes
Explained: BS 8500 (concrete).
Our checks use the guidance for England unless a badge says otherwise. Wales, Scotland and Northern Ireland have their own rules: check the source for where you live.