Quick Slab Design Calculator
Calculate reinforced concrete slab thickness and reinforcement per ACI 318 in seconds.
Input Parameters
Enter your slab dimensions and loading. Defaults: Dead load 1.0 kN/m², SDL 1.5 kN/m², SD40 steel, simply supported.
Need more power?
Sign up free to unlock AI recommendations, sustainability analysis, PDF reports, project saving, and 10 more calculators.
Get Started FreeHow This Slab Calculator Works
This calculator designs two-way reinforced concrete slabs using the moment coefficient method from ACI 318-19 (American Concrete Institute) and DPT 1008-61 (Thai Department of Public Works and Town & Country Planning). It determines minimum slab thickness based on deflection criteria, calculates factored moments in both directions using tabulated coefficients for different span ratios and support conditions, and selects reinforcement (bar size and spacing) that satisfies both strength and minimum steel requirements.
Key checks include deflection ratio (service load deflection vs. allowable L/240 or L/250), crack width estimation using a simplified Gergely-Lutz approach, and material quantity estimation for concrete volume and rebar weight. The design code strength reduction factor (phi = 0.9 for flexure) is applied per ACI 318-19.
Disclaimer: This tool is intended for preliminary design estimation only. All results must be verified by a licensed professional engineer before use in construction. The engineer of record bears full responsibility for the final design.