Rebar Calculator
Estimate how much reinforcement a slab needs: how many bars run each way, the total length to buy and the weight of steel involved.
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Formula and method
Bars are counted from the slab span divided by the spacing, plus one bar at each edge. Total length follows from the bar count, the slab dimensions, the number of layers and the waste allowance. Weight comes from the nominal mass per metre of the bar diameter.
How to measure the inputs
- Measure the slab length and width and confirm the designed bar spacing each way.
- Read the bar diameter from the design, for example 12 mm.
- Check how many layers of reinforcement are specified, one or two.
Worked example
Slab length 13.12 ft; Slab width 16.4 ft; Bar spacing (long direction) 3.28 ft; Bar spacing (short direction) 6.56 ft; Bar diameter 0.04 ft; Number of layers 2; Bar length (optional) 19.69 ft; Waste 10 % → Total bar length: 281.50 ft
Practical tips
- Order stock lengths that minimise cutting waste for your slab dimensions.
- Store rebar off the ground and keep it free of oil and mud.
- Tie bars at every intersection for the first row and then alternate.