Rebar Calculator
For a reinforced slab on a grid, this estimates the rebar — total linear feet, 20-foot sticks, and bar count — from the slab size and the spacing you choose.
Rebar
473linear ft
- 20-ft sticks
- 24 sticks
- Bars (both directions)
- 32 bars
This is a quantity estimate at a spacing you choose — NOT a structural design. Bar size, spacing, concrete cover, and lap lengths must follow engineered plans and local code.
How it’s calculated
Bars in each direction = ⌈ span ÷ spacing ⌉ + 1 (a bar at each edge). Linear feet = (bars running lengthwise × length) + (bars running crosswise × width), plus a lap/cut allowance. Sticks = linear feet ÷ 20, rounded up — rebar is sold in 20-foot sticks.
Worked example
A 20 × 10 ft slab on a 12-inch grid: ⌈10 × 12 ÷ 12⌉ + 1 = 11 bars the long way, ⌈20 × 12 ÷ 12⌉ + 1 = 21 the short way → 11 × 20 + 21 × 10 = 430 ft × 1.10 ≈ 473 ft = 24 twenty-foot sticks (32 bars).
FAQs
- What spacing should rebar be?
- 12 to 18 inches on center is common for residential slabs, but the right spacing and bar size come from the design loads, not a rule of thumb. Follow your engineered plan or local code.
- Does this size the rebar?
- No — it counts quantity at a spacing you choose. Bar size (#3, #4, #5…), spacing, concrete cover, and lap lengths are structural decisions for an engineer or a code table.
- Why the lap allowance?
- Rebar is spliced by overlapping bars (often 40 bar-diameters or more) and you cut waste at the ends. The waste percentage is a rough cushion for both — not a lap-length spec. Actual lap length is bar-size-dependent and an engineering value; raise the percentage for a slab with many splices.
Sources
- Bars per direction = ⌈span ÷ spacing⌉ + 1; linear ft = Σ(bars × run); sold in 20-ft sticks. Quantity/spacing estimate — geometry only, not a structural design.