Calculate how much rebar you need for your concrete slab. Free online rebar calculator with spacing, length, and weight estimation.
The rebar calculator estimates the amount of reinforcing steel needed for a concrete slab. Enter slab dimensions and desired bar spacing to get the number of bars, total length, and approximate weight. The calculator assumes #4 rebar (1/2" diameter) which weighs 0.668 lb/ft.
Bars = (Dimension / Spacing) + 1 | Total Length = Σ(Bars × Perpendicular Dimension) | Weight = Length × 0.668 lb/ftThe number of bars is calculated by dividing the perpendicular dimension by the spacing and adding 1 for the edge bar. Standard spacing is 12-18 inches for residential slabs. The weight is calculated using #4 rebar weight of 0.668 lb/ft.
| Input | Output |
|---|---|
| 20×15 ft slab, 18" spacing | 11 bars + 14 bars = 404 linear ft, 270 lbs |
| 30×20 ft slab, 12" spacing | 21 bars + 31 bars = 1,230 linear ft, 822 lbs |
| 10×10 ft slab, 16" spacing | 8 bars + 8 bars = 160 linear ft, 107 lbs |