Rebar Calculator

Formula

side = √areabarsPerDirection = ⌊(side × 12) / spacing⌋ + 1totalBars = barsPerDirection × 2totalBarsWithWaste = ⌈totalBars × (1 + waste/100)⌉totalLinearFt = ⌈totalBars × side × (1 + waste/100)⌉

Parameters

Spacing

12", 18", or 24" on center.

Rebar Size

#3 (3/8"), #4 (1/2"), #5 (5/8"), #6 (3/4").

Waste %

Extra for laps, bends, cut-offs. 10–15%.

Results

Bars

Total rebar pieces needed.

Linear Feet

Total rebar footage to order.

Example

side = √400 = 20 ftbarsPerDirection = ⌊(20 × 12) / 18⌋ + 1 = 14totalBars = 14 × 2 = 28totalBarsWithWaste = ⌈28 × 1.10⌉ = 31 barstotalLinearFt = ⌈28 × 20 × 1.10⌉ = 616 lf

Common Use Cases

• Garage and driveway slabs
• Foundation footings
• Retaining walls
• Pool decks

Notes

• Assumes square slab (√area). Rectangular pours are approximations.
• Does not account for overlap splices — add 10–15% waste.
• Standard rebar lengths: 20 ft sticks are most common at supply yards; some carry 30 ft, 40 ft, or 60 ft for big jobs. Smaller pieces can be cut on-site with a chop saw or bender.
• Lap splice rule of thumb: minimum 40× bar diameter (#4 lap ≈ 20", #5 lap ≈ 25"). ACI 318 covers exact requirements.

Frequently Asked Questions