About the Rebar Calculator
Reinforcing bar for a slab or footing — bar count, total length, weight and lap allowance.
Also known as: reinforcement calculator, steel bar calculator, rebar weight, reinforcing steel quantity.
How to use this calculator
- Enter slab length, slab width, bar spacing, bar size and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
bars = clear span ÷ spacing + 1, in each direction
Worked example
Using the values pre-filled in the calculator above:
- Slab length = 6 m
- Slab width = 4 m
- Bar spacing = 200 mm
- Bar size: 12 mm (0.888 kg/m)
- Concrete cover each side = 50 mm
- Layers: One layer
- Price per kg = 1.1
the calculator returns:
- Total bar length: 246.8 m
- Weight of steel: 219.1 kg
- Bars running lengthwise: 20
- Bars running crosswise: 30