| Primary value | 0.8 to 1.0 % of concrete volume (≈ 75–90 kg / m³) |
| Applies to | One-way and two-way RCC slabs · Roof and floor slabs in residential framing · Estimation of steel quantity at tender stage |
| Exceptions | IS 456 minimum (Fe500, main reinforcement) → 0.12% of gross area |
| IS 456 minimum (Fe415, main reinforcement) → 0.15% of gross area | |
| IS 456 maximum spacing → 300 mm or 3d, whichever is less | |
| Heavily loaded or longer-span slab → 1.0–1.2% | |
| Measured as | Volume of steel ÷ volume of concrete × 100. As a unit weight: 1% = 78.5 kg of steel per m³ of concrete. |
| Source | IS 456 — Clause 26.5.2 ✓ Verified |
68 related items across IS codes, knowledge articles, design rules, maps and tools
Slab steel % is the input every estimator needs to convert concrete volume into a rebar order. 0.8–1.0% covers the typical residential slab — anything below 0.5% will fail the IS 456 minimum and anything above 1.2% means the slab is undersized and being carried by reinforcement.
BBS engineers use 80 kg/m³ as their default factor for slab steel. The number trends to 1.0% in seismic zones III–V where additional bottom-bar continuity over supports is mandated by IS 13920.