How much rebar do I need? Calculate linear feet, number of sticks, weight, and cost for concrete slabs, footings, and walls. Enter your dimensions and rebar spacing for instant estimates.
Rebar Details
10% recommended for cuts, overlaps, and bends
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Enter your slab dimensions for rebar estimates
Last updated March 2026 by our expert review team
Steel supplier pricing. Hardware stores typically charge 30% to 50% more per foot.
Ehsan Ghazanfari
Licensed Structural Engineer
FISE-certified structural engineer with 11+ years designing bridges, retaining walls, and foundations. MSc from Aalto University.
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Certified Cost & Estimating Professional
AACE-certified estimator working with 20+ insulation companies including the two largest franchises in America.
See full profileUpdated March 2026
How we verify our calculators#4 rebar on 12-inch centers is the standard for residential slabs. It handles driveways, garage floors, and patios without overbuilding.
Overlap bars by 40 diameters at every splice. For #4 rebar (1/2 inch), that means 20 inches of overlap. Wire-tie the splice tightly so it does not shift during the pour.
Use rebar chairs or bolsters to hold the grid 2 inches above the bottom of the form. Rebar sitting on the ground does nothing for structural strength.
Pair this with our concrete slab calculator to figure out how much concrete you need for the same project.
For footings and foundation walls, check our concrete footing calculator for volume and sizing.
Always bend hooks at the ends of rebar in footings. A 90-degree hook at each end prevents the bar from pulling out of the concrete under load.
Buy rebar in 20-foot sticks from a steel supplier, not the hardware store. You will pay 30% to 50% less per foot and get cleaner cuts.
Store rebar off the ground on wood blocks and cover with a tarp. Surface rust is cosmetic, but heavy scale weakens the bond with concrete.
Enter the slab length, width, rebar size, and grid spacing. Select a waste factor for cuts and overlaps.
The calculator counts bars in each direction based on spacing, then multiplies by slab dimensions to get total linear feet.
Get total linear feet, 20-ft sticks needed, weight in pounds, tie wire rolls, and a cost range based on rebar size.
Formulas
Bars Lengthwise = floor(Width / Spacing) + 1
Bars Widthwise = floor(Length / Spacing) + 1
Total Linear Ft = (Bars Lengthwise x Length + Bars Widthwise x Width) x Waste
20-ft Sticks = Total Linear Ft / 20
What spacing should I use for rebar in a slab?
12 inches on center in both directions is standard for residential slabs (driveways, garages, patios). Heavy-duty commercial slabs may use 8-inch or 6-inch spacing.
What size rebar for a concrete slab?
#4 rebar (1/2 inch) is the standard for residential slabs 4 to 6 inches thick. Use #3 for light-duty patios and walkways. Use #5 or #6 for structural footings and thick slabs.
How much does rebar weigh per foot?
#3 rebar weighs 0.376 lbs/ft, #4 weighs 0.668 lbs/ft, #5 weighs 1.043 lbs/ft, and #6 weighs 1.502 lbs/ft. Multiply by total linear feet for the full weight.
How much overlap for rebar splices?
Overlap by 40 times the bar diameter. For #4 rebar, that is 40 x 0.5 inches = 20 inches. For #5, it is 40 x 0.625 = 25 inches. Wire-tie every splice.
Do I need rebar chairs or supports?
Yes. Rebar must sit at mid-depth in the slab, typically 2 inches from the bottom. Use plastic or metal rebar chairs every 3 to 4 feet to hold the grid in position during the pour.
Is rebar better than wire mesh?
Rebar is stronger and prevents cracks from spreading. Wire mesh only holds cracks together after they form. Use rebar for driveways, garage floors, and any slab that carries weight.
How much does a 20-foot stick of rebar cost?
A 20-foot stick of #4 rebar costs $10 to $18 at steel suppliers and $15 to $25 at hardware stores. Buying in bulk from a supplier saves significantly.
Do I need rebar in a 4-inch slab?
For a patio or walkway with no vehicle traffic, wire mesh is often enough. For any slab that supports vehicles, heavy loads, or sits on expansive soil, use #4 rebar on 12-inch centers.
A basic backyard patio. 11 bars each direction with 10% waste. Budget $110 to $198 for rebar alone.
Standard two-car driveway section. 13 bars lengthwise plus 21 widthwise. Budget $265 to $477 for material.
Full two-car garage floor. 25 bars in each direction creates a tight grid. Budget $634 to $1,140 for rebar.
Foundation perimeter footing with two continuous bars and 10% for lap splices. Budget $114 to $194 for #5 rebar.
Rebar sitting on the ground instead of on chairs
Rebar must be elevated to mid-depth in the slab. Without chairs every 3 to 4 feet, the bars sink to the bottom during the pour and provide zero reinforcement where it matters.
Insufficient overlap at splices
Bars that barely overlap will pull apart under stress. Always overlap by 40 times the bar diameter. For #4 rebar, that is a minimum of 20 inches with tight wire ties at each splice.
Wrong spacing for the application
Using 18-inch or 24-inch spacing on a driveway slab leaves too much unreinforced concrete between bars. Driveways and garage floors need 12-inch spacing maximum.
Cutting rebar without safety glasses
A rebar cutter or grinder throws metal fragments at high speed. Always wear safety glasses, gloves, and hearing protection when cutting or bending rebar.
Leaving rebar exposed to weather causing rust
Heavy rust and scale weaken the bond between rebar and concrete. Store bars off the ground on wood blocks, cover with a tarp, and use them within a few weeks of delivery.
Important Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.