Rebar Calculator for Concrete Slabs
Estimate how much rebar or welded wire mesh reinforcement you need for your concrete slab or footing. Enter your slab dimensions below — the calculator automatically shows rebar and mesh estimates.
Concrete Calculator
Select your project type, enter dimensions, and get instant results with bag counts, weight, and cost.
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60 lb Bags
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Total Weight
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At 1+ cubic yard, truck delivery ($125–$175/yd) is usually cheaper and easier than mixing bags by hand.
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Project Details
| Zone | Type | Dimensions | Qty | Volume (cu ft) |
|---|
Results
Total Volume — | Cubic Yards — | Total Weight — |
60 lb Bags — | 80 lb Bags — | Est. Cost — |
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Rebar Guide for Concrete Projects
When Do You Need Rebar?
- Any slab over 4 inches thick and larger than 8×8 feet
- Driveways and areas with vehicle traffic (always)
- Footings and foundations (required by code)
- Retaining walls (required by code)
- Stairs and elevated slabs (always)
Small patios on stable ground (under 100 sq ft) can often get by with wire mesh instead of rebar.
Common Rebar Sizes
| Size | Diameter | Weight/ft | Common Use |
|---|---|---|---|
| #3 | 3/8" | 0.376 lb | Light slabs, temperature steel |
| #4 | 1/2" | 0.668 lb | Standard slabs, footings (most common) |
| #5 | 5/8" | 1.043 lb | Foundation walls, heavy footings |
| #6 | 3/4" | 1.502 lb | Retaining walls, commercial |
Rebar Spacing Guidelines
- 12" on center (both ways) — standard for 4" residential slabs
- 18" on center — minimum for temperature/shrinkage steel
- 8" on center — driveways, heavy-load areas
- 6" on center — structural slabs, engineers' spec
Wire Mesh Alternative
Welded wire mesh (WWM) sheets are an easier alternative to rebar for smaller residential slabs:
- Standard sheet size: 4×8 feet (also available in 5×10 ft rolls)
- Common gauge: 6×6-W1.4×W1.4 (6" grid, light gauge)
- Overlap sheets by at least 6 inches
- Support mesh on chairs or stones — it must be in the middle or upper third of the slab
Rebar Calculator FAQ
When do I need rebar in a concrete slab?
Rebar is recommended for any slab over 8×8 feet, all driveways and garages (vehicle traffic), slabs over 4 inches thick, and any structural application. Small patios under 100 sq ft on stable ground can use welded wire mesh instead. All footings, foundations, walls, and stairs always require rebar reinforcement per building codes.
What size rebar for a 4-inch concrete slab?
#4 rebar (½-inch diameter) at 12-inch spacing in both directions is standard for 4-inch residential slabs. For driveways and heavy-traffic areas, tighten spacing to 8 inches on center. Place rebar in the middle third of the slab thickness (about 2 inches from the bottom) using rebar chairs or dobies to maintain position during the pour.
Can I use wire mesh instead of rebar?
Welded wire mesh (6×6 W1.4×W1.4) works for small residential patios under 100 sq ft and 4-inch thick slabs with only pedestrian traffic. For driveways, garages, structural slabs, or anything with vehicle traffic, rebar provides significantly stronger reinforcement. Mesh is also harder to keep properly positioned in the concrete during a pour — it tends to sink to the bottom where it does little good.
How much does rebar cost per foot?
#4 rebar costs $0.50-$0.80 per foot at home improvement stores (sold in 10-foot and 20-foot lengths). #5 rebar runs $0.70-$1.10 per foot. For a 10×10 slab with 12-inch spacing, you need about 220 feet of #4 rebar, costing $110-$175 total. Wire mesh sheets (4×8 ft) cost $8-$12 each — you'd need about 4 sheets for the same slab.
Related Tools
- Slab Calculator — calculate slab volume
- Footing Calculator — footing volume with rebar
- Wall Calculator — retaining wall volume
- Cost Calculator — total material estimate