Rebar calculator
Rebar Calculator — Linear Feet & Lap Allowances (2026)
How much rebar do I need for a slab? Counts #3, #4, or #5 deformed bars at 12 in or 16 in on-center across a 2-way grid, plus ACI 318 lap splices across 20 ft stock. Enter slab length, width, bar size, spacing, and number of identical slabs.
Pricing
Enter slab dimensions above to see bar count and lap allowances.
Rebar, chairs & tie wire on Amazon
Stock the bars the calculator above sized for the slab — plus the chairs that hold them centered and the wire that ties the grid together.
- Deformed #3 rebar (3/8 in × 20 ft) ↗
For 4 in residential slabs on stable soil.
- Deformed #4 rebar (1/2 in × 20 ft) ↗
Default for driveway and garage slabs — accounts for ACI 318 lap splices.
- Deformed #5 rebar (5/8 in × 20 ft) ↗
Heavier slabs and frost-susceptible regions.
- Plastic rebar chairs (3 in clearance) ↗
Keep the rebar centered in the slab — order one per 2 sq ft.
- 16-gauge rebar tie wire (3.5 lb roll) ↗
One roll ties every intersection on a 20 ft × 30 ft slab.
- Rebar tie wire twister tool ↗
One-handed twists save 30 seconds per cross — worth it past 200 intersections.
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Related calculators
- Concrete calculator
Cubic yards and bag counts for the slab the rebar reinforces.
- Studs calculator
Stud and plate linear feet for the framing around the same pour.