Rebar Spacing Calculator

Formula

side = √(area)netSide = side × 12 − 2 × coverbarsPerDirection = ⌊netSide / spacing⌋ + 1totalBars = barsPerDirection × 2 × layers × (1 + waste/100)totalLinearFt = totalBars × barLength × (1 + waste/100)weight = totalLinearFt × weightPerFt

Parameters

Rebar Size

#3 through #8 with weight per foot.

Spacing

Bar spacing on center (default: 12").

Edge Cover

Clearance from slab edge (default: 3").

Layers

Single (top or bottom) or double (both).

Waste %

Extra for overlaps and cuts.

Results

Bars per Direction

Bars running one way.

Total Bars

Both directions × layers, with waste.

Linear Feet

Total rebar length needed.

Weight

Total weight in pounds.

Example

side = 20 ft, netSide = 234 inbarsPerDirection = ⌊234/12⌋ + 1 = 20totalBars = (20+20) × 1 × 1.10 = 44linearFt = 44 × 19.5 = 858 lfweight = 858 × 0.668 = 573 lb

Common Use Cases

• Concrete slab reinforcement
• Foundation mat rebar layout
• Retaining wall reinforcement
• Pool and patio slab rebar

Notes

• Weight per foot: #3=0.376, #4=0.668, #5=1.043, #6=1.502, #7=2.044, #8=2.670 lb/ft.
• Double layer is common for structural slabs and foundations.
• Uses √(area) to approximate a square — adjust waste % for rectangular slabs.
• ACI 318 minimum cover (cast-in-place concrete): 3″ for concrete cast against earth, 2″ exposed to earth or weather, 3/4″ to 1-1/2″ interior depending on bar size.
• Chair / spacer rule of thumb: 1 chair per 5 sq ft of slab for #4 grids. Use 3″ or 4″ chairs to position rebar at the design depth before pouring.

Frequently Asked Questions