Free Rebar Calculator — Bars, Linear Feet & Weight (2026)

How to Use This Calculator

1. 1Enter the slab length and width in feet.
2. 2Set the desired bar spacing — 12" on center is common for residential slabs.
3. 3Select the rebar size: #3 for light-duty, #4 for standard residential, #5 for structural.
4. 4Click Calculate for bar count, linear feet, and total weight.

About This Material

Rebar (short for reinforcing bar) is deformed steel bar embedded in concrete to provide tensile strength that concrete alone cannot resist. Concrete is strong in compression but weak in tension — rebar bridges cracks and holds the slab together under load. The most common sizes for residential and light commercial work are #3 (3/8-inch diameter, 0.376 lbs/ft), #4 (1/2-inch, 0.668 lbs/ft), and #5 (5/8-inch, 1.043 lbs/ft). Standard rebar comes in 20-foot lengths. When a slab dimension exceeds 20 feet, bars must be spliced with an overlap of 40 bar diameters — that is 20 inches for #4 rebar. Grade 60 rebar (yield strength 60,000 psi) is the industry standard for residential construction throughout North America. It is available in plain (black) steel, epoxy-coated (green) for corrosive environments, and galvanized for marine or de-icing salt exposure. Epoxy-coated rebar costs roughly 30–50% more than plain steel but is required by many codes for garage slabs, driveways, and exterior flatwork exposed to road salt. Typical spacing is 12 inches on center in both directions for 4-inch residential slabs, 18 inches for lightly loaded patios, and 8 inches for driveways or structural slabs. Rebar must be elevated off the sub-base on wire chairs or plastic rebar supports so it sits in the lower third of the slab thickness — placing rebar on the ground provides zero structural benefit. Current pricing runs $0.50 to $0.90 per linear foot for #4 rebar, or roughly $10 to $18 per 20-foot stick. A typical 20×20-foot slab with #4 at 12-inch centers requires about 82 bars and 820 linear feet of rebar weighing approximately 548 lbs.

Installation Tips

• •Place rebar on wire chairs or plastic supports so it sits in the lower third of the slab — never lay bars directly on the ground.
• •Overlap splices by 40 bar diameters (20" for #4, 25" for #5) and secure with tie wire at every intersection.
• •Tie every rebar intersection with 16-gauge tie wire using a rebar tier or manual twisting tool.
• •Keep a minimum 3 inches of concrete cover on all sides to prevent corrosion of the steel.
• •Cut rebar with a rebar cutter or reciprocating saw with a metal blade — never use a torch, which weakens the steel.
• •Bend rebar cold using a manual or hydraulic rebar bender — heating weakens the bar and voids engineering ratings.

Common Mistakes to Avoid

• ⚠Laying rebar on the ground instead of elevating it on chairs — without proper placement the rebar provides no structural value.
• ⚠Insufficient splice overlap — splices shorter than 40 bar diameters will pull apart under load.
• ⚠Using the wrong rebar size — #3 is too light for driveways and garage slabs; use #4 minimum.
• ⚠Skipping tie wire at intersections — unsecured rebar shifts during the pour and ends up misaligned.
• ⚠Forgetting to account for waste — order 10–15% extra for cuts, bends, and overlaps.

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