Formula
d (min) = Span / (L/d Ratio × Steel Factor)
L/d: SS=20, Continuous=26, Cantilever=12
Overall = d + 20mm cover
4.5m continuous slab, Fe415:
d = 4500/(26×0.82) = 211mm → 215mm
Overall = 235mm → provide 250mm
Frequently Asked Questions
IS 456 specifies minimum 75mm for two-way slabs and 100mm for flat slabs. The L/d method usually governs for longer spans.
Span-to-effective-depth ratio controls deflection. IS 456 values: Simply Supported=20, Continuous=26, Cantilever=12, modified by steel grade factor.