Home & Construction · Building Materials
Concrete Calculator — Volume, Cement Bags, Sand & Aggregate
Work out the volume of concrete for a slab, footing, round column or flight of stairs in metric or imperial units, then the materials for a nominal mix (M10, M15, M20, M25 or your own ratio): 50 kg cement bags, sand and coarse aggregate in m³ and cubic feet, water, and the number of ready-mix bags if you're buying premix.
Your inputs
Quick start — try a typical case
A typical house roof slab is 0.125–0.15 m (5–6 in).
Your result Live
Concrete Needed
3 m³
105.9 cu ft · 3.92 cubic yards
- Cement (50 kg bags)
- 26 bags (25.4 exact, 1.27 tonnes)
- Sand
- 1.32 m³ · 47 cu ft
- Coarse Aggregate
- 2.65 m³ · 93 cu ft
- Water (approx.)
- 635 litres
- Mix Used
- 1 : 1.5 : 3 (cement : sand : aggregate), +5 % wastage
- Or Pre-mixed Bags
- 177 × 80 lb · 236 × 60 lb · 354 × 40 lb
- Cement · 18%0.88 m³
- Sand · 27%1.32 m³
- Aggregate · 55%2.65 m³
Dry materials are about 1.54× the wet volume because they shrink once mixed and the voids fill; a 50 kg bag of cement is about 0.0347 m³.
Nominal mixes suit small works. For structural RCC, follow your engineer's design mix (IS 456 / IS 10262) — M25 and above should be design mixes.
How this is calculated
Dry volume = wet volume × 1.54 × (1 + wastage) · Cement = dry × c ÷ (c + s + a) · Bags = cement m³ ÷ 0.0347
- c : s : a
- Mix ratio of cement, sand and coarse aggregate (M20 = 1 : 1.5 : 3)
- 1.54
- Dry-volume factor — the usual site allowance for bulking and voids
- Water
- Cement weight × water–cement ratio (0.5 → 25 litres per bag)
First find the wet volume of the pour. Mixing dry materials with water fills the gaps between grains, so you need about 54 % more dry material than the finished volume. Split that by the mix ratio to get the volume of cement, sand and aggregate; cement is then counted in 50 kg bags.
Assumptions & sources
- Nominal volumetric mix with a 1.54 dry-volume factor; cement bulk density 1,440 kg/m³.
- Stairs are treated as a solid flight resting on the ground (a waist slab needs less).
- US premix yields: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft, 40 lb ≈ 0.30 cu ft.
- 1IS 456:2000 — Plain and Reinforced Concrete, Code of Practice (Table 9, nominal mix proportions) — Bureau of Indian Standards
- 2How to calculate cement, sand and aggregates — Bricknbolt
Calculator ID HOME-CONCRETE-001 · version 1.0.0
Common questions
How many cement bags for 1 m³ of M20 concrete?
About 8 bags: 1.54 m³ dry × 1/5.5 = 0.28 m³ of cement ÷ 0.0347 m³ per bag.
How thick should a roof slab be?
For an ordinary house, 125–150 mm (5–6 inches) is common, but slab thickness depends on the span and loads — your structural engineer decides it.
Why add wastage?
Some concrete is always lost to spillage, uneven formwork and leftovers; 5–10 % is a sensible allowance.