Calculators/ Concrete/Rebar Calculator
Rebar Calculator
Rebar quantity and total length for a slab grid.
Rebar Calculator
ft
ft
in
in
Rebar in a slab is laid as a grid. This works out how many bars each direction needs at your chosen spacing, and the total linear feet to order.
How this is calculated
- Subtract the edge cover from both dimensions: rebar must not reach the slab edge, or it will rust and spall the concrete.
- Bars per direction = usable span ÷ spacing, plus one for the closing bar.
- Total linear feet is the sum of both directions. Rebar is sold in 20 ft lengths.
Frequently asked questions
What spacing should rebar be?
Eighteen inches on centre is standard for residential slabs. Twelve inches is used for heavier loads such as a garage or workshop floor.
What size rebar for a slab?
#4 rebar, which is half an inch, covers most residential slabs and driveways. #3 is sometimes used for footpaths and thin slabs.
How much cover does rebar need?
Three inches from any face exposed to soil, and about two inches elsewhere. Rebar sitting on the sub-grade does nothing: it must sit on chairs.