Rebar Calculator
Concrete & Masonry · Updated July 2026
Enter your slab dimensions and grid spacing to find how much rebar you need — total linear feet plus the number of bars in each direction.
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Estimates only. Add extra for waste and confirm with your supplier.
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How much rebar do I need for a slab?
Space bars in a grid (commonly 12–18 inches apart) in both directions. Count the bars each way, multiply by their length, and add for total linear feet.
Laying out a rebar grid
Rebar is placed in a grid running both directions across a slab. Count the bars each way (grid spacing plus one), multiply by their length, and add for total linear feet. Standard residential spacing is 12–18 inches on center.
Placement tips
Support bars on chairs so steel sits in the middle third of the slab thickness, and overlap splices by about 40 bar diameters. Keep rebar at least 3 inches from the ground and edges so concrete fully encases it.
How to use this calculator
- 1Measure your slab length and width in feet.
- 2Choose your grid spacing in inches (12–18 is typical).
- 3Read total linear feet and bar counts from the results.
Frequently asked questions
What spacing should rebar be?
12–18 inch on-center spacing is common for residential slabs. Tighter spacing adds strength for heavier loads.
What spacing should rebar be in a slab?
12–18 inches on center is typical for residential slabs; tighter spacing adds strength for heavier loads.
How much should rebar overlap?
Overlap splices by roughly 40 times the bar diameter — about 20 inches for #4 (½ in) rebar.
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