Calculators
Rebar Calculator
Calculate rebar for a slab grid: bars in each direction, total linear feet, sticks to buy with lap splices, and weight.
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The tool
Enter your numbers below. Results update as you type, and nothing leaves your browser.
Everything you enter stays on your own machine. Nothing is sent to us or to anyone else, which you can confirm in your browser network tab.
What people use it for
- Ordering rebar for a slab or patio
- Pricing reinforcement
- Checking an engineer's schedule
- DIY slab projects
About this tool
What the Rebar Calculator does
A slab reinforcing grid has bars running both ways at a set spacing, kept back from the edges by concrete cover. Count the bars in each direction, multiply by their length, and allow extra for lap splices where bars join. Weight follows from the bar size.
It also works as a rebar spacing calculator.
Formula
- Bars in one direction = (span − 2 × cover) × 12 ÷ spacing + 1
- Linear feet = Σ bars × bar length (+ lap splices for bars longer than a stick)
- Weight = linear feet × weight per foot (e.g. #4 = 0.668 lb/ft)
Worked example
Using the starting values in the calculator above:
| Input | Value |
|---|---|
| Slab length | 20 ft |
| Slab width | 10 ft |
| Bar spacing | 12 in |
| Edge cover | 3 in |
| Stick length | 20 ft |
| Bar size | #4 (1/2 in) |
| Lap splice length | 2 ft |
| Result | Value |
|---|---|
| Sticks to buy | 20 |
| Total linear feet | 385 |
| Bars running lengthwise | 10 |
| Bars running widthwise | 20 |
| Weight | 257 |
How to read the result
Rebar must sit in the middle or lower third of the slab on chairs or dobies, not on the ground, to do its job.
Spacing, bar size and lap lengths should follow your engineer’s drawings or local code.
Quantities are estimates. Check product data sheets and local codes, and confirm with your supplier before ordering.
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Questions
Questions about this tool
The things clients actually want to know — costs, timelines, ownership and what happens after launch.
Count bars in each direction from the spacing, multiply by their lengths and add lap splices.
Residential slabs often use 12 to 18 inches on centre, but follow the design.
About 0.668 lb per foot.
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