Rebar Calculator
Calculate how many rebar bars you need for a slab or footing, and the total linear feet of steel - for both single and double-direction (grid) reinforcement.
How to use this rebar calculator
Enter the length and width of the concrete pour, the spacing between bars, and choose single or grid reinforcement. The calculator divides the run by the spacing, adds one for the starting bar, and multiplies by the bar length to give you total linear feet.
For a one-way layout (typical for small footings) use "single direction". For slabs, driveways and patios, use "grid" - bars run both ways, roughly doubling the amount of steel. Standard practice is #3 bars (3/8 inch) at 12-18 inches on center for residential work.
Rebar calculator FAQ
How many linear feet of rebar is in a 10x10 slab?
With #3 rebar at 12-inch spacing in both directions, a 10x10 slab needs about 10 bars of 10 feet each way - 220 linear feet total including both directions.
What is the difference between #3 and #4 rebar?
#3 rebar is 3/8-inch diameter and #4 is 1/2-inch. Use #4 (or larger) for footings, foundations and structural pours; #3 is fine for most residential flat slabs.
Do I need rebar chairs or spacers?
Yes - rebar must sit in the middle third of the slab, not at the bottom. Use plastic chairs every 3-4 feet so the bar is fully embedded in concrete and protected from moisture.