What is M20 / M25 Concrete? | Q & A

M20 and M25 are grades of concrete, where:

• “M” = Mix

• Number (20 / 25) = Characteristic compressive strength of concrete in N/mm² (MPa) after 28 days of curing.

1. Meaning of M20 Concrete

• Grade: M20

• Characteristic strength: 20 N/mm² (20 MPa) at 28 days

• Typical nominal mix (by volume):
  1 : 1.5 : 3
  (Cement : Fine Aggregate : Coarse Aggregate)

Common Uses:

• Slabs (residential buildings)

• Beams (low-rise structures)

• Footings

• PCC + RCC works (basic structures)

2. Meaning of M25 Concrete

• Grade: M25

• Characteristic strength: 25 N/mm² (25 MPa) at 28 days

• Mix type: Design mix (not fixed ratio)

Common Uses:

• RCC columns

• Beams and slabs with higher loads

• Foundations

• Most modern RCC structural members

3. Key Difference Between M20 and M25 AspectM20M25

28-day strength	20 MPa	25 MPa
Mix type	Nominal mix	Design mix
Cement content	Lower	Higher
Load capacity	Moderate	Higher
Usage	Residential / light structures	Structural RCC works

4. Important Interview Points

• M20 is the minimum grade recommended for RCC (as per IS 456).

• Higher grade → higher strength, durability, and cost.

• Strength is verified by cube test at 28 days.

5. One-Line Interview Answer (Best)

M20 and M25 are grades of concrete where the number indicates the characteristic compressive strength in N/mm² at 28 days—20 MPa for M20 and 25 MPa for M25.