The grade of concrete M-15 means that the compressive strength of a 15 cm cube after 28 days is ...........
Try it first: pick an option, then read the explanation.
Correct answer: B. 150 kg/cm²
M-15 Strength in kg/cm²
Convert M15’s characteristic strength from N/mm² to kg/cm²:
Step 1. M15 → fck = 15 N/mm²
Step 2. Conversion: 1 N/mm² = 1 MPa = 10.197 kg/cm² ≈ 10.2 kg/cm²15 × 10.2 = 153 kg/cm² ≈ 150 kg/cm²
M-15 corresponds to 150 kg/cm² — option B.
Key takeaway
Quick rule: multiply N/mm² by 10 to get approximate kg/cm². M15 → 150, M20 → 200, M30 → 300.