Construction Basics
Concrete Grades Explained: Which Grade to Use at Each Stage of Building Construction
Concrete is the backbone of any building, but not all concrete is the same. The "grade" of concrete tells you how strong it is, and different parts of a building need different grades. Using the wrong grade can waste money or, worse, compromise safety. This guide explains concrete grades in plain language and where each one is typically used in home construction.
What does a concrete grade mean?
Concrete grades are written as M10, M15, M20, M25 and so on. The "M" stands for the mix of cement, sand and coarse aggregate (jelly), and the number is the concrete''s characteristic compressive strength in N/mm² (MPa) after 28 days of curing, as defined by the Indian Standard IS 456:2000.
So M20 concrete is designed to withstand a load of 20 N/mm². The higher the number, the stronger — and generally the more cement-rich and expensive — the mix.
Grades up to M25 are usually made as nominal or design mixes batched at site, while M30 and above are design mixes worked out by an engineer for the specific materials being used.
Common grades and where they are used
| Grade | Strength (N/mm²) | Typical use in a house |
|---|---|---|
| M5 – M7.5 | 5 – 7.5 | Levelling course below foundations, non-structural filling |
| M10 | 10 | Plain Cement Concrete (PCC) below footings and under floor slabs |
| M15 | 15 | PCC works, flooring base, pathways, non-load-bearing works |
| M20 | 20 | Minimum grade for RCC — slabs, beams, columns, footings of small houses |
| M25 | 25 | RCC in multi-storey homes, heavily loaded slabs and beams |
| M30 and above | 30+ | Design mixes for taller buildings, long spans, special structural needs |
Stage-by-stage: which grade goes where
1. Foundation bed (PCC below footings)
Before any reinforcement is laid, a thin layer of Plain Cement Concrete is poured on the excavated soil. This is called PCC or "mud mat". It gives a clean, level surface and stops the footing concrete from mixing with soil.
- Typical grade: M10 (sometimes M7.5 or M15 depending on soil and design)
- This layer is not structural, so a lower grade is sufficient.
2. Footings and foundations
Footings carry the entire load of the building into the ground. They are reinforced (RCC), so they need structural-grade concrete.
- Typical grade: M20 minimum; M25 for larger loads or multi-storey buildings
- IS 456 specifies M20 as the minimum grade for reinforced concrete work.
3. Plinth beam
The plinth beam ties all the columns together at ground level and supports the walls above. It also protects against differential settlement.
- Typical grade: M20 or M25
4. Columns
Columns are the vertical members that transfer load from slabs and beams down to the footings. They are among the most critical elements in the building.
- Typical grade: M20 for a single-storey house; M25 or higher for additional floors, as advised by the structural engineer
5. Beams
Beams span between columns and carry the slab and wall loads.
- Typical grade: M20–M25, matching the columns and slab design
6. Roof slab (RCC slab)
The roof slab is the largest concrete pour in a house and must be cast in one go with proper vibration and curing.
- Typical grade: M20 is common for residential slabs; M25 where spans are longer or loads are higher
7. Staircase
The staircase slab and waist slab are structural RCC elements.
- Typical grade: M20–M25
8. Lintel and chajja (sunshades)
Lintels sit over door and window openings; chajjas project out to shade openings from sun and rain.
- Typical grade: M20, though small non-structural elements may use M15
9. Floor screed and PCC flooring
The base under your floor finish (tiles, granite, etc.) is usually plain concrete, not RCC.
- Typical grade: M10–M15 for the base; the wearing screed on top is a richer cement mortar, not structural concrete
10. Water tank, sump and retaining walls
Underground sumps and overhead tanks need concrete that resists water seepage. Here, the grade matters along with proper waterproofing admixtures and dense, well-compacted concrete.
- Typical grade: M20–M25 with waterproofing treatment
Why you should not simply use a higher grade everywhere
It is tempting to think "stronger is always better", but that is not true:
- Cost: Higher grades use more cement, increasing cost with no structural benefit where it is not needed.
- Cracking: Very rich mixes generate more heat while setting and can crack if not cured properly.
- Design balance: A structural engineer designs each element for the load it actually carries. The grade, steel and dimensions work together — changing one without the others can be unsafe.
What matters as much as the grade
Even the right grade fails if site practice is poor. Insist on:
- Correct water–cement ratio — extra water makes concrete easy to pour but weak.
- Proper vibration/compaction — removes air pockets that weaken the member.
- Curing for at least 7–14 days — concrete gains strength only while it stays moist.
- Cube testing — for larger pours, test cubes are cast and crushed at 7 and 28 days to verify the strength achieved.
- Good materials — clean sand, well-graded jelly, fresh cement and clean water.
The takeaway
As a rule of thumb for residential construction in Bangalore: M10–M15 for plain (PCC) works, M20 as the minimum for all structural RCC, and M25 or design mixes where the engineer specifies. The exact grades for your home should come from your structural engineer''s design, based on soil conditions, spans and the number of floors.
If you are planning a home and want clarity on materials, grades and specifications before you sign a contract, talk to our engineering team — we are happy to walk you through it.