Rebar Calculator — Quantity & Weight
Calculate the number of rebar bars, total lineal footage, and weight for any concrete slab, footing, or wall. Supports #3 through #8 rebar with adjustable spacing and a configurable waste factor for lap splices and end cuts.
Enter Dimensions
Add 10% for standard cuts and overlaps
Results
Bars Needed
38bars
Total Lineal Feet
608lin ft
Total rebar length including waste
Total Weight
406lb
#4 rebar weight per CRSI
Slab Area
240sq ft
Editorial Standards
Each calculator is reviewed for formula accuracy, unit consistency, and alignment with current U.S. building practices before publication. We verify outputs against published engineering references and real-world project data. Learn more about our methodology.
Rebar comes in 20-foot sticks and it's a hassle to make another run mid-pour. Nail the count before you set up — slab dimensions, bar spacing, and size are all you need.
For most residential work, #4 at 12-inch on-centerin both directions is the go-to spec for driveways, patios, and light footings. Structural applications — foundation walls, retaining walls, beams — usually call for #5 or heavier at tighter spacing per your engineer's drawings.
Specialized Versions
How the Rebar Calculator Works
The calculator places a grid of rebar in both directions across the slab. For each direction, the number of bars is: Ceiling(Slab Width ÷ Spacing) + 1 and Ceiling(Slab Length ÷ Spacing) + 1.
Bar weights come from CRSI published tables — multiply bar count by pounds-per-foot for your size to get the total weight.
If you also need to calculate the concrete volume for the slab itself, use the Concrete Slab Calculator to get cubic yards and bag counts for the pour.
Rebar Weight Reference (per CRSI)
| Rebar Size | Diameter | Weight (lb/ft) | Common Use |
|---|---|---|---|
| #3 | 3/8 in | 0.376 | Light slabs, driveways |
| #4 | 1/2 in | 0.668 | Standard residential slabs |
| #5 | 5/8 in | 1.043 | Footings, heavy slabs |
| #6 | 3/4 in | 1.502 | Columns, structural walls |
| #7 | 7/8 in | 2.044 | Structural beams |
| #8 | 1 in | 2.670 | Heavy structural members |
Pro Tips
- Order in 20-foot sticks. Standard rebar comes in 20-foot lengths. If your slab is 18 feet wide, each bar needs one stick with 2 feet of waste — not two sticks. Factor this into your cut list before ordering.
- Use rebar chairs. Set bars on plastic or concrete rebar chairs (dobies) to hold them 1.5–2 inches off the subgrade. Rebar lying on dirt provides almost no tensile benefit because it ends up in the compression zone.
- Tie intersections. Wire-tie every crossing with rebar tie wire and pliers. Untied bars shift during the pour, moving them out of position where the concrete is placed.
- Bump spacing for long walls. If your wall length is not divisible by your spacing, bump down to the next smaller spacing rather than running a bare edge with no bar. A consistent 10-inch OC grid is better than 12 OC with a 4-inch gap at the perimeter.
Common Mistakes
- Forgetting lap splices. Where two bars meet end-to-end, they must overlap by 40× the bar diameter (20 inches for #4). Omitting this from your estimate will leave you short on a large pour.
- Using #3 where #4 is required. #3 rebar is appropriate for light sidewalk slabs and thin decorative pads only. Most driveways and structural slabs require #4 minimum — verify with your local building department before ordering.
- Measuring over obstacles. If columns, drain pipes, or sleeves interrupt the grid, you still count bars as if the slab were solid, then deduct only the bars that physically cannot be placed. Deducting too many leaves gaps in reinforcement coverage.
Rebar Grades, Specifications, and Alternatives
Not all rebar is equal. Grade, coating, and form factor all affect structural performance and ordering decisions.
Grade 40 vs Grade 60
Rebar is graded by its minimum yield strength in ksi (thousands of pounds per square inch). The two grades you will encounter at lumber yards and steel suppliers are:
| Grade | Yield Strength | Marking | Common Use |
|---|---|---|---|
| Grade 40 (ASTM A615/A615M-24) | 40,000 psi | No extra line or number | Residential slabs, light footings |
| Grade 60 (ASTM A615/A615M-24) | 60,000 psi | One line or "4" marking | Structural walls, beams, columns |
| Grade 60W (ASTM A706) | 60,000 psi (weldable) | "W" marking | Seismic zones, welded connections |
Grade 60 is the default for most structural applications and is what most suppliers stock. Grade 40 may be cheaper but requires more bars to achieve the same reinforcement — your structural engineer will specify which to use. For DIY residential slabs without an engineer, Grade 60 #4 at 12-inch OC is the safe default.
Epoxy-Coated Rebar
In coastal environments, bridge decks, parking garages, or anywhere road salt or marine air can reach the concrete, epoxy-coated (green) rebar resists corrosion. It costs 25–40% more per pound but can double the service life of the slab. Specify ASTM A775 or A934 when ordering.
Welded Wire Mesh (WWM) as an Alternative
For light-duty flatwork — sidewalks, patios, thin decorative slabs — welded wire mesh (WWM) is a faster alternative to individual rebar bars. Common specs:
- 6×6 W1.4×W1.4 (formerly 6×6 10/10) — the standard residential-grade mesh. Provides similar reinforcement to #3 rebar at 18-inch spacing. Best for 3.5–4-inch slabs not subject to vehicle traffic.
- 6×6 W2.9×W2.9 (formerly 6×6 6/6) — heavier mesh equivalent to #3 at 12-inch spacing. Use for 4–5-inch slabs with light vehicle traffic.
WWM is sold in rolls (5 ft × 150 ft) or sheets (5 ft × 10 ft). Sheets are easier to handle and position on chairs; rolls are more economical for large areas. Overlap adjacent sheets by one mesh square (6 inches) at all edges.
2025–2026 Rebar Retail Pricing
Rebar prices fluctuate with the steel market and import tariff policy. Current U.S. retail ranges at lumber yards and home improvement stores (per HomeGuide/HomeAdvisor, 2025–2026):
| Bar Size | Diameter | Price / LF | Price / 20 ft Stick | Notes |
|---|---|---|---|---|
| #3 | 3/8 in | $0.45–$0.70 | ~$9–$14 | Light slabs, sidewalks |
| #4 | 1/2 in | $0.65–$0.95 | ~$13–$19 | Standard residential |
| #5 | 5/8 in | $1.00–$1.45 | ~$20–$29 | Driveways, footings |
| #4 epoxy | 1/2 in | $0.85–$1.35 | ~$17–$27 | Coastal/salt environments |
Prices reflect 2025–2026 U.S. retail. Steel import tariffs enacted in 2025 have applied modest upward pressure on domestic rebar; budget 10–15% higher than 2023 baseline pricing. Buying in full bundles (typically 1,000 lb) from a steel service center reduces cost by 15–25% versus retail sticks.
Frequently Asked Questions
How much rebar do I need per square foot of concrete slab?
For a standard 12-inch OC grid with #4 rebar, plan on roughly 2 bars per square foot (running both directions).
What rebar size should I use for a concrete driveway?
#3 or #4 rebar is standard for residential driveways. Use #3 (3/8 in) for lightly loaded slabs 4 inches thick, and #4 (1/2 in) for 5–6 inch slabs that carry vehicles. Always check local building codes for your specific application.
What is the standard rebar spacing for a concrete slab?
12 inches on center is the most common spacing for residential slabs. Driveways and patios often use 18-inch spacing for lightly loaded conditions. Foundation slabs and structural applications typically use 6-inch spacing with larger bars.
How do I calculate rebar weight for a concrete pour?
Multiply total lineal feet by the weight per foot for your size. Per CRSI: #3 = 0.376 lb/ft, #4 = 0.668 lb/ft, #5 = 1.043 lb/ft.
How much overlap do rebar bars need?
Standard lap splice is 40× the bar diameter — 20 inches for #4. A 10% waste factor covers typical lapping and end cuts.
Can this calculator be used for walls and footings?
Yes — enter the wall height as 'slab length' and the wall width as 'slab width' to calculate rebar for a rectangular footing or wall section. Adjust the spacing to match your structural drawings.