Rebar Calculator
Calculate the number of rebar pieces, total linear feet, and weight needed for concrete slab or footing reinforcement. Enter your slab dimensions, bar spacing, and rebar size for a complete material takeoff.
Slab / Footing Dimensions
Full Breakdown
Slab Area
Bars (length direction)
Bars (width direction)
Total Linear Feet
Stock Bars to Buy
Total Weight
Lap Splice Length
How to Use This Calculator
- Enter the length and width of your concrete slab or footing.
- Select the bar spacing (12″ O.C. is common for residential slabs).
- Choose the rebar size (#4 is most common for residential).
- Set the stock bar length (standard is 20 ft).
- Choose grid (both directions) or one-way layout.
- Click "Calculate Rebar" for your material list.
The Formula
Bars in length dir. = ⌊Width ÷ (Spacing/12)⌋ + 1
Bars in width dir. = ⌊Length ÷ (Spacing/12)⌋ + 1
Total Linear Ft = (Bars_L × Length) + (Bars_W × Width)
Stock Bars = ⌈Total Linear Ft ÷ Bar Length⌉
Weight = Total Linear Ft × Weight per Ft
Lap Splice = 40 × Bar Diameter (ACI 318)
Bars in width dir. = ⌊Length ÷ (Spacing/12)⌋ + 1
Total Linear Ft = (Bars_L × Length) + (Bars_W × Width)
Stock Bars = ⌈Total Linear Ft ÷ Bar Length⌉
Weight = Total Linear Ft × Weight per Ft
Lap Splice = 40 × Bar Diameter (ACI 318)
Bar weights: #3 = 0.376, #4 = 0.668, #5 = 1.043, #6 = 1.502, #7 = 2.044, #8 = 2.670 lb/ft. Lap splice uses ACI 318 minimum of 40 bar diameters for tension splices.