What this calculator does
Rebar for a concrete slab works out bar count and total length for a two-way rebar grid in a slab or footing. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaBars one way = ⌊dimension / spacing⌋ + 1; each bar is cut to the length of the opposite dimension
The inputs explained
| Field | What to enter |
|---|---|
| Slab length (m) | A number, measured in m. Starts at 6. |
| Slab width (m) | A number, measured in m. Starts at 4. |
| Grid spacing (mm) | A number, measured in mm. Starts at 300. |
| Standard bar length (m) | A number, measured in m. Starts at 6. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with slab length
Every other input is held at the calculator’s starting values while slab length varies. Select any row to load that scenario into the calculator.