For 100 cft of 1:2:4 concrete you need about 17.9 bags of cement, 44 cft of sand and 88 cft of crush. For one cubic metre it is about 6.3 bags, 15.5 cft of sand and 31.1 cft of crush.
Pick what you are casting and enter its size. The calculator turns the wet volume into dry materials with a factor of 1.54, splits it by the mix, and prices it at your cement, sand and crush rates.
Materials per 100 cft of concrete
Wet volume of 100 cft, dry volume factor 1.54, one 50 kg bag = 1.226 cft.
| Mix | Cement (bags) | Sand (cft) | Crush (cft) | Typical use |
|---|---|---|---|---|
| 1:1.5:3 | 22.8 | 42.0 | 84.0 | Columns, beams and slabs where the engineer asks for a richer mix |
| 1:2:4 | 17.9 | 44.0 | 88.0 | Most house roof slabs, beams and columns |
| 1:3:6 | 12.6 | 46.2 | 92.4 | Plain concrete (PCC) under foundations and floors |
Per cubic metre the figures are about 8.1 bags for 1:1.5:3, 6.3 bags for 1:2:4 and 4.4 bags for 1:3:6.
How to calculate cement, sand and crush
Take the slab loaded above: 30 ft x 25 ft, 5 inches thick, 1:2:4.
- Wet volume: 30 x 25 x 5/12 = 312.5 cft (8.85 cubic metres).
- Dry volume: loose cement, sand and crush shrink when water is added and voids fill, so multiply by 1.54: 312.5 x 1.54 = 481.25 cft.
- Parts: 1 + 2 + 4 = 7.
- Cement: 481.25 / 7 = 68.75 cft. One bag is 50 kg, and at 1,440 kg per cubic metre that is 1.226 cft, so 68.75 / 1.226 = 56.1 bags.
- Sand: 481.25 x 2/7 = 137.5 cft.
- Crush: 481.25 x 4/7 = 275 cft.
At Rs 1,450 a bag, Rs 80 a cft for sand and Rs 130 for crush, the materials cost Rs 128,061. Steel, shuttering, water and labour are extra.
Some engineers use 1.52 or 1.57 instead of 1.54. The difference is about 2%.
Which mix to use
- 1:2:4 is the usual mix for house roof slabs, beams and columns.
- 1:1.5:3 is richer and stronger. Engineers specify it for heavily loaded columns and beams.
- 1:3:6 is lean plain concrete (PCC), used under footings and floors where there is no steel.
Follow the mix on your structural drawings. Crush is usually 3/4 inch (about 20 mm) for slabs and beams. Too much water makes concrete weak whatever the mix, so do not add water on site to make it flow.
Columns and beams
For eight columns 9 x 12 inches and 10 ft high, choose "Beam or column", enter 10 ft, 9 inch and 12 inch, and 8 pieces. The wet volume is 8 x 10 x 0.75 x 1 = 60 cft, which needs about 10.8 bags of cement, 26.4 cft of sand and 52.8 cft of crush at 1:2:4.
For the steel in the same work, use the steel weight calculator. For the whole house, the construction cost calculator estimates everything from the covered area.
Concrete questions
How many cement bags are in 1 cubic metre of 1:2:4 concrete?
About 6.34 bags of 50 kg. The dry volume is 1.54 cubic metres, cement is one seventh of that, 0.22 cubic metres, and one bag is 0.0347 cubic metres. Sand is 0.44 and crush 0.88 cubic metres.
How many cement bags are needed for 100 cft of concrete?
About 17.9 bags at 1:2:4, 22.8 bags at 1:1.5:3 and 12.6 bags at 1:3:6. Round up when you buy, and add 2% to 5% for spillage if the formwork is uneven.
Why multiply by 1.54 for dry volume?
Dry cement, sand and crush contain air gaps. When mixed with water, the fine particles fill the gaps between the stones, so the finished concrete is smaller than the dry pile. About 1.54 volumes of dry material make one volume of set concrete.
How much concrete is in a 5 inch slab?
5/12 of a cft for every sq ft of slab, or 0.417 cft. A 1,000 sq ft roof slab 5 inches thick is 417 cft, which at 1:2:4 needs about 75 bags of cement, 183 cft of sand and 367 cft of crush.
Last reviewed 30 September 2026. Results are estimates; official notices always take precedence.