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 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. In metres that’s 3.048 × 3.658 × 0.127 = 1.42 m³ of wet concrete. Dry volume = 1.42 × 1.54 = 2.18 m³. Cement gets 1/7 of that, so 0.31 m³ of cement = 8.98 bags → 9 bags. Sand is 2/7 of the dry volume = 23 cft, and aggregate is 4/7 = 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.
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 1.42 m³ of wet concrete. With a 1:2:4 mix, plan for roughly 9 bags of 50 kg cement, 23 cft of sand and 45 cft of aggregate — plus 5–10% extra for wastage.