Concrete Calculator — Cement Bags, Sand & Aggregate
Enter the size of your slab, footing, column or beam, pick a mix ratio, and instantly find out how many cement bags, sand (cft) and aggregate to order.
Cement bags required
–
50 kg bags, rounded up
Sand (fine aggregate)
–
cubic feet
Aggregate (coarse)
–
cubic feet
Wet concrete volume
–
cubic metres
How to use it
- Measure the pour: the length, width and depth of the slab, footing, column or beam you are casting.
- Enter the three dimensions above and set the unit toggle — feet or metres, the same unit for all three.
- Pick the mix ratio your engineer specified; 1:2:4 (M15) is pre-selected for floors and PCC work.
- Click Calculate.
- Order the cement bags (already rounded up), sand (cft) and aggregate (cft) shown — plus 5–10% extra for spillage.
How this concrete calculator works
You buy concrete ingredients in bags and truckloads, but you plan the pour in cubic feet or metres. This calculator converts one into the other. Enter the finished (wet) size of what you’re casting — a slab, footing, column or beam — and it works backwards to the raw materials using the standard dry-volume method. Dry volume means the total space the loose cement, sand and stone occupy before water is added.
The formula
When you mix concrete, cement and sand fill the gaps between the stones — so the loose ingredients take up more space than the finished pour. Here’s the thumb rule:
- Wet volume = length × width × depth (all converted to metres)
- Dry volume = wet volume × 1.54
- Cement volume = dry volume × cement parts ÷ total parts
- Cement bags = cement volume ÷ 0.0347, rounded up (one 50 kg bag ≈ 0.0347 m³)
- Sand / aggregate (cft) = dry volume × their share × 35.3147
Worked example
Let’s work through a real example: a 10 ft × 12 ft slab, 5 inches (0.42 ft) thick, in a 1:2:4 mix — exactly the values pre-filled in the form above. In metres that’s 3.048 × 3.658 × 0.128 = 1.43 m³ of wet concrete. Dry volume = 1.43 × 1.54 = 2.20 m³. Cement gets 1/7 of that, so 0.314 m³ of cement = 9.05 bags → 10 bags. Sand is 2/7 of the dry volume = 22.18 cft, shown rounded up as 23 cft, and aggregate is 4/7 = 44.35 cft, rounded up to 45 cft.
Notes for Indian sites
Sand dealers in India usually quote per brass (100 cft) or per truckload — so convert your cft figure to brass before you call. Always order 5–10% extra: spillage and uneven shuttering eat into your material, and a small buffer stops you running out mid-pour. For RCC work (slabs, beams, columns), stick to the grade your structural engineer specified — a weaker mix saves a little cement but risks the whole structure. And check the manufacturing date on every cement bag, then use it within 90 days. Old cement loses strength.
Materials per cubic metre, by mix
Here is what one cubic metre of finished (wet) concrete takes under each mix this calculator offers, using the same dry-volume method. Cement is the exact figure — the calculator rounds bags up for your pour size.
| Grade | Mix (cement : sand : aggregate) | Cement bags per m³ | Sand (cft) per m³ | Aggregate (cft) per m³ | Typical use |
|---|---|---|---|---|---|
| M7.5 | 1:4:8 | 3.41 | 16.7 | 33.5 | Bedding, levelling |
| M10 | 1:3:6 | 4.44 | 16.3 | 32.6 | Foundations |
| M15 | 1:2:4 | 6.34 | 15.5 | 31.1 | Floors, PCC, pathways |
| M20 | 1:1.5:3 | 8.07 | 14.8 | 29.7 | RCC slabs, beams, columns |
Another worked example — in metres, with M20
Switch the unit toggle to metres and enter a 3 m × 4 m RCC slab, 0.15 m (150 mm) thick, with the 1:1.5:3 (M20) mix. Wet volume = 3 × 4 × 0.15 = 1.80 m³. Dry volume = 1.80 × 1.54 = 2.77 m³. The mix has 5.5 total parts, so cement = 2.77 × 1/5.5 = 0.504 m³, which is 0.504 ÷ 0.0347 = 14.5 → 15 bags. Sand = 2.77 × 1.5/5.5 = 0.756 m³ = 26.7 cft, shown rounded up as 27 cft. Aggregate = 2.77 × 3/5.5 = 1.512 m³ = 53.4 cft, rounded up to 54 cft.
Frequently asked questions
How many cement bags are needed for 1 cubic metre of concrete?
It depends on the mix ratio. For 1:2:4 (M15), 1 m³ of wet concrete needs about 1.54 m³ of loose dry materials. Cement's share is 1/7 of that — 0.22 m³, or roughly 6.34 bags. So order 7 bags of 50 kg cement per cubic metre of 1:2:4 concrete.
What does a 1:2:4 concrete mix ratio mean?
It means 1 part cement, 2 parts sand and 4 parts coarse aggregate, measured by volume. This is the standard M15 grade mix — the one used for flooring, PCC and non-structural work in Indian homes.
Why is the volume multiplied by 1.54 in concrete estimation?
When mixed, cement and sand fill the gaps between the stones, so wet concrete takes up less space than its loose ingredients. The factor 1.54 converts wet volume into dry volume — the total space of the loose materials before mixing. Indian quantity surveyors use this thumb rule every day.
Which concrete mix should I use for a house slab in India?
Use M20 grade (1:1.5:3) for RCC roof slabs, beams and columns — or whatever your structural engineer specifies. 1:2:4 (M15) suits PCC, flooring and pathways. Never use a lower grade than your engineer specified just to save cement.
How much concrete do I need for a 10 ft × 12 ft slab, 5 inches thick?
That slab works out to about 1.43 m³ of wet concrete. With a 1:2:4 mix, plan for roughly 10 bags of 50 kg cement, 23 cft of sand and 45 cft of aggregate — plus 5–10% extra for wastage.
How do I convert cubic feet into brass?
Divide by 100 — one brass is exactly 100 cft, the unit sand and aggregate dealers across much of India quote in. This calculator already shows the brass figure under the sand and aggregate results, so 45 cft appears as about 0.45 brass.