Rebar Calculator
Enter your dimensions for an instant answer — the exact quantity to buy (waste included), a material cost, and an estimated installed cost. Change any figure to update the result live.
| ITEM | QTY | PRICE RANGE |
|---|---|---|
| linear ft | 344 | $223.6–$550.4 |
| Estimated material total | $223.6–$550.4 |
- Grid: 13 + 13 bars at 12 in on-center
How much rebar do I need for a slab?
Enter the slab length, width and your grid spacing — 12 inches on-center is the common residential default. The calculator counts the bars running each direction (span ÷ spacing, plus one), multiplies by their lengths, and adds 10% for the overlaps where bars are lapped and tied.
The result is total linear feet plus the bar count for your grid, so you can price 20-foot sticks of #4 rebar straight from the number.
Formula & methodology
linear ft = (bars along length × length) + (bars along width × width), + 10% laps
Bars per direction are floor(span ÷ spacing) + 1. The 10% allowance covers the 12–18 inch overlap at every lap splice.
All constants are published on the material reference; the full model is on the methodology page.
12 ft × 12 ft slab, 12 in grid: you need 312 linear ft (buy 344 with waste), about $223.6–$550.4 in materials. See how we calculate this →
Popular sizes
Rebar cost
#4 rebar runs $0.65–$1.60 per linear foot nationally; slab reinforcement is usually priced into the concrete pour.
rebar cost by state →Frequently asked questions
How much rebar do I need for a slab?
For a grid at the chosen spacing, add up the bars running each direction. A 12×12 slab on a 12-inch grid needs about 312 linear feet — buy roughly 344 with lap overlaps included.
What spacing should rebar be?
Residential slabs typically use a 12 to 18 inch grid; 12 inches on-center is the safe default for driveways and garage slabs. Tighter spacing adds strength but uses more bar — change the spacing input above to compare totals.
What size rebar for a slab?
Residential slabs commonly use #3 or #4 (3/8" or 1/2") rebar on a 12–18 inch grid.
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