Slab Minimum Reinforcement
Rectangular slab to AS3600:2018 + Amdt 2. Flexural minimum, shrinkage & temperature steel, bar suggestions. Free, no login.
Preliminary tool, not certified engineering advice. Verify results against AS3600:2018 and obtain independent review before relying on any output. Certley accepts no liability for use of this calculator.
How it works
This calculator determines the minimum reinforcement required in a concrete slab to AS3600:2018 Section 9. Enter the slab depth, effective depth, concrete grade, and the expected degree of crack control, and it returns the governing minimum steel area per metre strip with practical bar-and-spacing options that satisfy the standard.
What it calculates
Flexural minimum (Cl 9.1.1) uses the characteristic flexural tensile strength f'ct.f = 0.6√f'c and the ratio (Ds/d)² to compute the minimum reinforcement ratio p.min, then converts it to a steel area Ast.flex.min for the strip width.
Shrinkage and temperature steel (Table 9.5.3) sets a secondary reinforcement rate based on the degree of crack control (minor, moderate, or strong) and whether the slab is restrained. The primary direction must carry at least 75% of this secondary requirement.
The governing minimum is the larger of the flexural minimum and 75% of the secondary requirement. The calculator then suggests N10 through N20 bars at spacings rounded to 25 mm increments, filtered by the AS3600 maximum spacing limits for the selected crack-control level.
Verify with a registered engineer
Minimum reinforcement is a starting point. Actual slab design requires checking bending, shear, deflection, and detailing for the full load case. Need it certified? Get a quote from a Certley engineer.