Rebar Calculator
Slab length and width are feet. Spacing and edge clearance are inches. Bars form a single mat. Weight uses lb per foot (default 0.668 for #4 class). Estimate only, not a permit, code check, or engineered design.
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How to estimate rebar
- Enter slab length and width in feet.
- Enter bar spacing and edge clearance in inches.
- Confirm or change lb per foot for your bar size (default 0.668).
- Read bars each way, total linear feet, and steel weight sketch. Laps and chairs stay out.
Slab rebar mat
Single grid with edge clearance
| Inner length | lengthIn - 2 × edgeClearance |
|---|---|
| Bars // length | floor(innerW / spacing) + 1 |
| Bars // width | floor(innerL / spacing) + 1 |
| Total LF | barsAlongLength × lengthFt + barsAlongWidth × widthFt |
| Weight | total LF × lbPerFt |
| Default lb/ft | 0.668 (#4 class sketch) |
How bar length and weight are computed
Convert length and width to inches. Inner sizes subtract twice the edge clearance. Count bars each way from spacing. Total LF multiplies counts by the slab sides in feet. Weight multiplies LF by lbPerFt.
Bar size, laps, and chairs
Change lbPerFt for #3, #5, or metric bars using a supplier table. Lap splices add length this page does not include. Chair height and cover belong on the drawings. Metal stock weight helpers sit on metal weight.
Use cases
A 20 by 20 ft slab at 12 in spacing with 3 in clearance and #4 lb/ft. Comparing 12 versus 18 in spacing. Not a stamped reinforcing schedule.
Limits
No lap percent, no hooks, and no dual mat. Estimate only, not a permit, code check, or engineered design. Nothing is uploaded.