Rebar Calculator for Concrete Slab
Estimated Total Cost
$787 – $1,404
For 400 sq ft slab (20' × 20')
Linear Feet
704
20' Bars
36
Total Weight
470 lbs
Material Cost
$387 – $704
Labor Cost
$400 – $700
Placement: Position rebar on chairs at 1/3 to 1/2 slab thickness from bottom. Overlap bars 40× diameter (15" for #3, 20" for #4) at splices.
Not included: Rebar chairs/supports ($0.25–$0.50 each), tie wire, concrete cost, forming, finishing. Consider wire mesh ($0.15–$0.30/sqft) as an alternative for light-duty slabs.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Rebar Cost & Size Guide
| Size | Diameter | Cost/Foot | Best For |
|---|---|---|---|
| #3 | 3/8" | $0.40 – $0.75 | Sidewalks, patios |
| #4 | 1/2" | $0.55 – $1.00 | Driveways, garages, 4" slabs |
| #5 | 5/8" | $0.75 – $1.35 | 6" slabs, heavy loads |
| #6 | 3/4" | $1.00 – $1.75 | Footings, foundations |
* Material cost only. Add $1.00–$1.75/sqft for labor installation.
Example Projects
| Project | Size | Rebar Needed | Est. Cost |
|---|---|---|---|
| Patio | 12×12 ft, #3 @ 18" | ~200 linear ft | $80 – $150 |
| Driveway | 20×20 ft, #4 @ 12" | ~900 linear ft | $500 – $900 |
| Garage Floor | 24×24 ft, #4 @ 16" | ~950 linear ft | $520 – $950 |
| Shop Floor | 30×40 ft, #5 @ 12" | ~2,650 linear ft | $2,000 – $3,600 |
* Includes 10% waste factor. Actual costs depend on local steel prices.
How We Calculate
Our rebar calculator estimates linear feet, bars, and cost based on slab dimensions, rebar size, and spacing. Total linear feet = (length ÷ spacing + 1) × width + (width ÷ spacing + 1) × length × 1.10 waste factor.
Grid calculation: Bars run in both directions to form a grid. The number of bars in each direction = (perpendicular dimension ÷ spacing) + 1. Bars should overlap 40× their diameter at splices.
Rebar Size Guide
#3 (3/8") — Sidewalks, patios, light duty. $0.40–$0.75/ft. #4 (1/2") — Driveways, garage floors, 4" slabs. $0.55–$1.00/ft. #5 (5/8") — Heavy-duty, 6" slabs, shop floors. $0.75–$1.35/ft. #6 (3/4") — Footings, structural. $1.00–$1.75/ft.
Spacing Recommendations
12" o.c. — Driveways, heavy loads. 16" o.c. — Standard for most slabs. 18" o.c. — Patios, walkways. 24" o.c. — Light duty, minimal reinforcement.
Additional Costs
Rebar chairs: $0.25–$0.50 each. Tie wire: $5–$15/roll. Labor: $1.00–$1.75/sqft installed. Wire mesh alternative: $0.15–$0.30/sqft.
Data Sources
Pricing from HomeGuide, HomeAdvisor, and steel supplier quotes (February 2026). Installation labor from contractor surveys.
Last updated: 2026-02-05
Frequently Asked Questions
How much rebar do I need for a concrete slab? +
Rebar quantity depends on slab size and spacing. For a 20×20 ft slab with 16" spacing, you need about 600 linear feet of rebar. Calculate: (length/spacing + 1) × width + (width/spacing + 1) × length, plus 10% waste.
What size rebar for a 4-inch slab? +
#3 (3/8") or #4 (1/2") rebar is standard for 4" slabs. Use #3 for patios and sidewalks, #4 for driveways and garage floors. #4 is more common as it provides better crack resistance for minimal extra cost.
How much does rebar cost per foot? +
Rebar costs $0.40–$1.75 per linear foot depending on size. #3 rebar costs $0.40–$0.75/ft, #4 costs $0.55–$1.00/ft, #5 costs $0.75–$1.35/ft, and #6 costs $1.00–$1.75/ft. Buy in bulk for better pricing.
What spacing should rebar be for a driveway? +
Driveways should have rebar at 12" on center spacing with #4 rebar for vehicle loads. Lighter-duty areas like patios can use 16–18" spacing. Never exceed 24" spacing for any slab.
Do I need rebar or wire mesh for a patio? +
For patios, either works. Wire mesh ($0.15–$0.30/sqft) is cheaper and easier for DIY. Rebar provides stronger reinforcement for larger slabs or areas that may see heavy loads. For slabs over 500 sqft, rebar is preferred.
How do you place rebar in a concrete slab? +
Place rebar on chairs or supports at 1/3 to 1/2 the slab thickness from the bottom (about 1.5" up for a 4" slab). Create a grid pattern with bars overlapping 40× the bar diameter at splices. Tie intersections with wire.
Can I use fiber mesh instead of rebar? +
Fiber mesh reduces surface cracking but doesn't replace structural reinforcement. It's not a substitute for rebar in driveways or garage floors. Use fiber mesh as an addition to rebar for extra crack control, not as a replacement.
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