Cement calculator for concrete, plaster and brickwork
This cement calculator answers the question every site asks first: how many bags of cement do I need? Choose the job — a concrete slab, footing or floor, wall or ceiling plaster, or a brick wall — enter the size and the mix ratio, and it gives the cement in 50 kg bags (or 25 kg, 40 kg and 94 lb US bags), the sand and, for concrete, the coarse aggregate and water. Add prices and it totals the material cost.
All three jobs use the nominal-mix method of Indian estimators: wet volume, plus waste, times a dry-volume factor, split in the mix ratio. Every factor is shown and editable.
How to use the Cement Calculator
- Choose metric or imperial units and what the cement is for: concrete, plaster or a brick wall.
- Enter the size: length and width (or wall length and height) with the thickness, or the area. For concrete you can also type a known volume, such as 1 m³.
- Pick the mix ratio. Choosing a job loads typical values — 1 : 2 : 4 concrete, 12 mm plaster at 1 : 6, a 230 mm wall in 1 : 6 mortar — which you can edit.
- Check the waste allowance, dry volume factor and bag size, and add prices if you want a cost.
- Read the bags, sand and aggregate, and copy the summary for your supplier.
Cement Calculator features
Three jobs, one method
Concrete, plaster and brick masonry mortar, each with its usual dry-volume factor and waste allowance.
IS 456 checks
Per-m³ cement, aggregate and water per 50 kg bag compared with Table 9 for nominal mixes up to M20.
Every unit
Bags and kg of cement; sand in m³, cft, brass, tonnes and cubic yards; metric or imperial inputs.
Material cost
Cement per bag, sand and aggregate per m³, cft, brass, tonne, yd³ or US ton, in your currency.
How the cement is worked out
Cement is then converted at 1,440 kg/m³, so one 50 kg bag is 0.0347 m³. Example: a 4 × 3 m slab 100 mm thick is 1.2 m³; with 5 % waste 1.26 m³; dry volume 1.26 × 1.54 = 1.94 m³; cement = 1.94 ÷ 7 = 0.277 m³ = 399 kg, or 8 bags, with 0.55 m³ (19.6 cft) of sand and 1.11 m³ of 20 mm aggregate.
The dry-volume factors are site conventions, not code values: loose sand and aggregate have voids, and sand bulks when damp, so more material goes in than the finished volume. Some estimators use 1.52 or 1.57 for concrete and 1.27–1.35 for mortar.
| Job | Wet volume | Dry factor | Split |
|---|---|---|---|
| Concrete | length × width × thickness | 1.54 | cement : sand : aggregate |
| Plaster | area × thickness, + 20 % for joints and unevenness | 1.27 | cement : sand |
| Brick wall | wall volume minus the bricks (about 23 % mortar with 10 mm joints) | 1.33 | cement : sand |
Cement bags per cubic metre of concrete
IS 456:2000 clause 9.3 allows nominal mixes only for M20 or lower; M25 and above must be designed (IS 10262:2019 gives the method), so the 1 : 1 : 2 row is a rough planning figure. The calculator compares your mix with Table 9 — aggregate and water per 50 kg bag — using the bulk densities you enter. For reinforced concrete, IS 456 Table 5 also sets a minimum of 300 kg of cement per m³ and M20 in mild exposure. Check the latest IS edition before relying on a clause.
| Mix | Grade | Cement per m³ | IS 456 Table 9 |
|---|---|---|---|
| 1 : 3 : 6 | M10 | 4.4 bags (222 kg) | nominal mix, max 480 kg aggregate per bag |
| 1 : 2 : 4 | M15 | 6.3 bags (317 kg) | nominal mix, max 330 kg aggregate, 32 L water per bag |
| 1 : 1.5 : 3 | M20 | 8.1 bags (403 kg) | nominal mix, max 250 kg aggregate, 30 L water per bag |
| 1 : 1 : 2 | “M25” | 11.1 bags (554 kg) | not a nominal mix — design mix required |
Plaster and brickwork rules of thumb
- 12 mm internal plaster at 1 : 6 takes about 0.08 bags per m² (roughly 1 bag per 140 sq ft); 20 mm external plaster at 1 : 4 about 0.18 bags per m².
- A one-brick (230 mm) wall in 1 : 6 mortar needs roughly 1.3 bags of cement per m³ of brickwork; 1 : 4 mortar about 1.8 bags.
- Bricks per m³ come from the brick size plus the joint: modular 190 × 90 × 90 mm bricks with 10 mm joints give 500 per m³. Add breakage separately.
- For full brick counts with wall faces and openings use the brick calculator; for plaster cost per wall the plaster calculator; for columns and stairs the concrete calculator.
Cement Calculator FAQ
How many cement bags are needed for 1 m³ of M20 concrete?
About 8.1 bags of 50 kg (403 kg) for a 1 : 1.5 : 3 nominal mix with the 1.54 dry-volume factor. Choose “I know the volume”, type 1 and set waste to 0 to see it.
How much cement do I need for a slab?
Multiply length × width × thickness for the volume, then use about 6.3 bags per m³ for 1 : 2 : 4 or 8.1 bags for 1 : 1.5 : 3. A 10 × 10 ft slab 4 in thick (0.94 m³) needs about 6 bags of M15 or 8 bags of M20 before waste.
How much cement is needed for plastering 100 sq ft?
At 12 mm and 1 : 6 with 20 % extra and a 1.27 factor, about 35 kg — under one 50 kg bag. At 20 mm and 1 : 4 it is about 82 kg.
Why is the dry volume 1.54 times the wet volume?
Loose cement, sand and stone contain air gaps that disappear when concrete is mixed and compacted, so you need roughly 54 % more loose material than the finished volume. It is a rule of thumb, which is why the factor is editable.
Is a 1 : 1 : 2 mix the same as M25?
Not formally. IS 456 lists nominal mixes only up to M20. M25 and stronger concrete should be a design mix tested in a lab; 1 : 1 : 2 is often quoted as a site approximation.
Does it work with US 94 lb bags?
Yes. Switch to imperial units and choose the 94 lb bag; areas are in square feet, thicknesses in inches and volumes in cubic yards.