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Slab Thickness Calculator
Minimum RCC slab thickness for one-way, two-way and flat slabs from the spans, per ACI 318 — with practical sizes for houses in Pakistan.
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About this calculator
Work out the minimum thickness of a roof or floor slab from its clear spans and slab type, and the practical thickness to use.
How it's calculated
- One-way: L/20, L/24, L/28 or L/10 (cantilever)
- Two-way on stiff beams: h = ln (0.8 + fy/200,000) ÷ (36 + 9β), ≥ 3.5″
- Flat slab: ln/33 (Grade 60), ≥ 5″
How thick should a house roof slab be?
Usually 5″ for rooms up to about 14 ft and 6″ for 15–18 ft rooms, confirmed by the structural design.
Results are calculated from the values you enter using standard formulas. Download the PDF to keep a record. For certified testing, design or construction, talk to our engineers.
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