About

Reinforcement is the backbone of a monolithic slab, providing tensile strength that concrete lacks alone. The steel grid (mesh) controls cracking due to thermal expansion and shrinkage while distributing structural loads. A properly designed grid must meet minimum reinforcement area requirements relative to the slab's cross-section.

This tool calculates the necessary steel reinforcement based on slab thickness and standard safety codes (typically 0.15% to 0.20% of the cross-sectional area). It visualizes the grid layout, calculates overlaps for joining bars, and verifies if your selected bar diameter and spacing meet the minimum structural criteria.

Formulas

Code requirements typically dictate that the Area of Steel ($A_s$) must be a minimum percentage of the gross concrete Area ($A_c$).

1. Minimum Steel Area ($A_{s,min}$):

A_s,min = 0.002 × b × h

2. Provided Steel Area ($A_{prov}$):

A_prov = 1000Spacing × A_bar

3. Overlap Length ($L_o$):

L_o ≈ 40 × d_bar

Reference Data

Rebar Size (Metric)	Diameter (mm)	Weight (kg/m)	Cross-Section Area (mm²)
#3 / φ10	10	0.617	78.5
#4 / φ12	12	0.888	113.1
#5 / φ14	14	1.210	153.9
#6 / φ16	16	1.580	201.1
#8 / φ25	25	3.850	490.9

Frequently Asked Questions

This ratio represents the minimum amount of steel required to control shrinkage cracks. If the steel area falls below this threshold, the concrete may crack excessively as it cures and shrinks, compromising the slab's durability and water resistance.

Common spacing for residential slabs is 200mm x 200mm (approx 8 inches). For heavier loads or thinner slabs, spacing might be reduced to 150mm. Spacing wider than 300mm is generally not recommended for structural slabs as it leaves large unreinforced patches.

The calculator checks the total steel area. For slabs thicker than 150mm, it is standard practice to place two layers of mesh (top and bottom). The tool assumes a single layer for calculation but recommends double layers for slabs >150mm.