About this calculator
Lay out a reinforcing grid for a slab. The calculator counts runs in each direction, stock bars including laps, steel weight, tie points and chairs.
How it’s calculated
Runs in each direction = floor(inside width ÷ spacing) + 1. A run longer than one stock bar needs laps of 40 bar diameters. Weight uses the nominal mass per foot for the bar size.
Worked example
With these inputs:
- Slab length
- 30 ft
- Slab width
- 20 ft
- Bar spacing (centres)
- 18 in
- Edge cover
- 3 in
- Bar size
- #4 (½")
- Stock bar length
- 20 ft
- Waste allowance
- 5%
the result is:
- Stock bars to order
- 51 bars
- Bars running lengthwise
- 14 runs × 29' 6"
- Bars running widthwise
- 20 runs × 19' 6"
- Lap length (40 × bar dia)
- 20"
- Total bar length incl. laps
- 826.3 lin ft
Tips from the trade
- Lap and cover requirements come from your engineer or local code. 40d is a common default, not a rule.
- Not every crossing has to be tied. Many crews tie every other one. The tie-wire count here assumes every crossing.
- Keep bars in the middle third of the slab with chairs. Rebar lying on the ground does nothing.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and local building codes before ordering.