Quick answer
The Rebar Calculator shows total rebar length and number of bars for a slab grid. How it works: Bars each way = side ÷ spacing + 1; Total length = bars × bar length, plus waste for laps. For example, with length of 20 ft, width of 20 ft, and bar spacing of 12 in, the stock bars to buy is 47.
How to use the Rebar Calculator
- Enter length.
- Enter width.
- Enter bar spacing.
- Enter stock bar length.
- Enter extra for waste. Adds a margin for cuts, spills, and uneven ground.
- Read stock bars to buy and the breakdown. Use Share to send the exact numbers, or Print to save a PDF.
How it's calculated
- Bars each way = side ÷ spacing + 1
- Total length = bars × bar length, plus waste for laps
Worked example
With length of 20 ft, width of 20 ft, bar spacing of 12 in, stock bar length of 20 ft, and extra for waste of 10 %:
Stock bars to buy: 47. Total length: 924 ft.
Questions people ask
Does this include lap splices?
The waste margin covers some overlap. Long runs need more; check your engineer's lap length.