RC Slab Rebar Calculator
Enter slab size, main and distribution bar spacing and diameter to compute bar counts and total steel weight (kg) using the d²/162 per-metre formula for slab reinforcement takeoff.
Input Data
Results
At a glance:Rebar per-metre weight (kg/m) ≈ diameter²(mm) ÷ 162, from steel density 7,850 kg/m³ circular section. Main bars run along the slab width: count = ⌊slab width(mm) ÷ spacing⌋ + 1, single length ≈ slab length − 2×cover. Distribution bars run along length: count = ⌊slab length(mm) ÷ spacing⌋ + 1, single length ≈ slab width − 2×cover. Total weight = (main total length + distribution total length) × respective per-metre weight.
Formula
Per-metre weight = d² / 162 (kg/m)
Main bars = ⌊(width×1000)/spacing⌋ + 1
Distribution bars = ⌊(length×1000)/spacing⌋ + 1
Total weight = Σ(bars × net length × per-metre weight)
$$w = \frac{d^2}{162}$$$$n_m = \left\lfloor \frac{W\cdot 1000}{s_m} \right\rfloor + 1$$$$n_d = \left\lfloor \frac{L\cdot 1000}{s_d} \right\rfloor + 1$$$$W_s = (n_m L_r + n_d W_r)\, w$$How to Use
- Enter the slab length and width.
- Enter the main bar spacing and diameter.
- Enter the distribution bar spacing and diameter.
- Enter the cover thickness.
- The tool outputs main bars, distribution bars and total steel weight.
Case Studies
Residential slab
5×4 m, main Ø12@200, distribution Ø10@200, cover 20 mm.
Main 21 bars × 3.96 m, distribution 26 bars × 4.96 m; total about 90 kg.
Roof slab
6×3 m, main Ø16@150, distribution Ø10@200.
Main 21 bars, distribution 41 bars; total about 200 kg.
FAQ
What is d²/162?
A common simplified rebar per-metre weight: circular cross-section × density (7,850 kg/m³) ÷ 1,000,000, giving d²/162 kg/m with d in mm.
Why deduct cover?
Cover is the concrete between rebar and surface; net bar length = slab dimension − 2×cover, so the steel does not reach the edge.
Main vs distribution bars?
Main bars carry the primary moment along the short span; distribution bars spread local loads and control cracking along the long span.
Related Tools
References
Content review: Calculatorism Construction Team. Results are for reference only; please refer to the relevant authorities for the official figures.