Enter your 28-day cube results and grade — get mean, standard deviation, CV and the full IS 456:2000 Table 11 (Amendment 4) conformity verdict: groups of four, individual limits, and small-pour criteria.
Comma, space or newline separated. Groups of four are taken consecutively from the top.
IS 456 Table 11 verdict
Mean and sample standard deviation (σ, n−1 basis) come straight from your numbers. Acceptance follows IS 456:2000 Table 11 as amended through Amendment 4: each group of four non-overlapping consecutive results must average at least fck + max(0.825σ rounded to the nearest 0.5, 3), and every individual result must be at least fck − 3. For pours of 30 m³ or less with fewer than four samples, Note 2 applies: mean ≥ fck + 4 and individual ≥ fck − 2.
The σ used is your established value if entered; otherwise the assumed values of Table 8 apply — 3.5 (M10–M15), 4.0 (M20–M25), 5.0 (M30+) N/mm² — which the code permits until a site σ from 30+ results is established.
Given: M25, results 34, 36, 38, 33 N/mm² (one group of four), no established σ → Table 8 σ = 4.0.
Mean = 35.25; sample σ = 2.22; CV = 6.3%
Group limit = 25 + max(round½(0.825 × 4.0), 3) = 25 + max(3.5, 3) = 28.5 → 35.25 ≥ 28.5 ✓
Individual limit = 25 − 3 = 22 → minimum 33 ≥ 22 ✓ → conforms
IS 456 judges conformity on the mean of four non-overlapping consecutive results — consecutive in order of sampling, so the check tracks production over time, not a hand-picked set. Enter results in the order the cubes were cast; this tool slices them into groups of four from the top.
Once you hold 30 or more results for the grade and plant, compute the actual σ and enter it — a well-controlled plant typically shows σ of 2–4 N/mm², comfortably below the assumed 4.0–5.0, which relaxes the group-mean limit and rewards good control.
Table 11 Note 2: for concrete quantity up to 30 m³ where fewer than four samples are taken, the mean must be at least fck + 4 and each individual result at least fck − 2. Tick the small-pour box to apply these limits. A single sample must itself be at least fck + 4.
A failed Table 11 check does not automatically mean rejection: IS 456 Cl 16.4 permits investigation of the actual structure — typically non-destructive testing (UPV, rebound hammer) or core extraction per IS 516 Part 4 / IS 456 Cl 17. The failure report should trigger an investigation of batching, sampling and testing before any removal decision.
Often used together with this calculator — pick the next step in your design or QA loop.
Deep dive: read the full significance guide — the code clauses, assumptions and site meaning behind these numbers.