Calculate the number of cement bags, sand and aggregate needed for a concrete or mortar mix by ratio.
Cement is the grey powder that binds a mix together; “concrete” is cement plus sand plus aggregate (gravel/stone), while “mortar” is just cement and sand. Choose your mix, enter the length, width and depth of the pour or bed, add a little waste, and read off the bags of cement, sand and aggregate you need.
| Ratio | Use |
|---|---|
| 1:2:4 | General-purpose concrete, paths, bases |
| 1:1.5:3 | Stronger structural concrete, footings |
| 1:3:6 | Mass fill and foundations |
| 1:4 (cement:sand) | General bricklaying mortar |
For 1 m³ of 1:2:4 concrete you need roughly 300 kg cement (≈ 6 × 50 lb / 12 × 25 kg bags), 0.5 m³ sand and 1 m³ aggregate. Cement is sold in 94 lb bags in the US and 25 kg bags in the UK — 40 × 25 kg bags make a tonne.
Tip: buy cement last and keep it dry — even a little moisture ruins it before you start.
A standard 1:2:4 concrete mix needs roughly 14 bags of 25 kg cement per cubic metre, along with about 0.7 m³ of sand and aggregate combined.
Cement is the powder binder. Concrete is cement mixed with sand and coarse aggregate plus water. This calculator shows how much of each you need.
Use 1:2:4 for general concrete, 1:1.5:3 for stronger structural work, 1:3:6 for foundations, and 1:4 to 1:6 cement to sand for mortar.
For a 1:2:4 mix, each 25 kg bag of cement needs roughly 50 kg of sharp sand and 100 kg of coarse aggregate — about two parts sand and four parts gravel to one part cement by volume.
Concrete made with ordinary Portland cement is touch-dry within a few hours, reaches initial set in 24–48 hours, and gains most of its strength after 28 days. Keep it damp while curing for the best result.
