The test strength of the sample is taken as the average of the strength of:

🟪 Number of Specimens for Test Strength

As per IS 456:2000 (Clause 15.4), the test strength of a concrete sample is the average of three specimens taken from the same batch and tested at the same age. A specimen’s result is accepted only if it lies within ±15% of the average; otherwise the result is suspect and further investigation is needed.

Key takeaway

Three cubes per sample per age is the IS 456 requirement. If one cube deviates by >15% from the average of three, it is excluded from the result.