Construction
Concrete Mix Ratios: M10, M15, M20, M25 and Cement Bags per Cubic Metre
What concrete grades mean, the mix ratio for each, cement bags, sand and aggregate per m³, and a worked roof-slab example.
By Team Vind · Updated · 5 min read
"M20", "1 : 1.5 : 3", "8 bags per cubic metre": concrete comes with its own shorthand. Knowing what the grades mean and how to turn a volume into cement bags, sand and aggregate lets you check a contractor's estimate and order the right quantities.
What M20 means
The M stands for mix, and the number is the concrete's strength in N/mm² (megapascals) after 28 days of curing. M20 concrete can carry 20 N/mm². For small jobs, Indian practice uses nominal mixes: fixed ratios of cement to sand to aggregate by volume.
Mix ratios by grade
| Grade | Cement : sand : aggregate | Used for |
|---|---|---|
| M10 | 1 : 3 : 6 | Levelling (PCC) under footings and floors |
| M15 | 1 : 2 : 4 | Floors, pathways, non-structural work |
| M20 | 1 : 1.5 : 3 | Slabs, beams, columns and footings in homes (minimum for RCC) |
| M25 | 1 : 1 : 2 | Columns, heavily loaded RCC, multi-storey buildings |
From volume to materials
Dry volume = wet volume × 1.54
Dry cement, sand and stone have air gaps that disappear when water is added, so you need about 54% more dry material than the finished concrete. Split the dry volume by the ratio, and divide the cement share by 0.0347 m³ (the volume of a 50 kg bag).
| Grade | Cement (50 kg bags) | Sand | Aggregate (20 mm) |
|---|---|---|---|
| M10 | 4.4 | 16.3 cft | 32.6 cft |
| M15 | 6.3 | 15.5 cft | 31.1 cft |
| M20 | 8.1 | 14.8 cft | 29.7 cft |
| M25 | 11.1 | 13.6 cft | 27.2 cft |
Try it: Concrete Calculator
Concrete Needed
Working
- Wet volume = 2.5 m³ × 1 + 5% wastage = 2.625 m³
- Dry volume = 2.625 × 1.54 = 4.043 m³
- Mix 1 : 1.5 : 3 (5.5 parts): cement = 4.043 × 1/5.5 = 0.735 m³ ÷ 0.0347 = 21.2 bags
Worked example: a roof slab
A 12 × 10 ft slab, 5 inches thick: 12 × 10 × 0.417 ft = 50 cft, or 1.42 m³. With 5% wastage, M20 needs about 12 bags of cement, 22 cft of sand and 44 cft of aggregate. Steel is extra; see steel weight per metre.
Site tips
- Use clean, well-graded sand; silt and clay weaken concrete.
- Measure with a box (farma), not by the head pan, so ratios stay consistent.
- Place within about 30 minutes of mixing, and compact with a vibrator to remove air pockets.
- For pours above about 3 m³, ready-mix concrete (RMC) is usually more consistent.
Budgeting a whole house? See materials for a 1,000 sq ft house.
Frequently asked questions
What is the ratio of M20 concrete?
1 : 1.5 : 3 (cement : sand : aggregate) by volume as a nominal mix.
How many bags of cement are in 1 m³ of M20?
About 8.1 bags of 50 kg, with roughly 15 cft of sand and 30 cft of aggregate.
Which concrete grade is used for a house slab?
M20 is the minimum for RCC slabs, beams and columns in houses. M25 is common for columns and multi-storey buildings.
Why is 1.54 used in concrete calculation?
Dry materials contain air gaps that fill when water is added, so about 54% more dry material is needed than the finished wet volume.
Sources
- IS 456:2000, Plain and reinforced concrete: code of practice (nominal mixes, minimum grades)
- IS 10262:2019, Concrete mix proportioning: guidelines
Last reviewed: 10 October 2026