30×20 ft slab, 12 in spacing, 2 ft laps, #4 rebar
- Bars‖length ≈ 21
- Bars‖width ≈ 26
- Linear ft ≈ 1,126
- Weight ≈ 752 lb
construction calculator
Slab Rebar Calculator
Lay out rebar grids for slabs or pads using spacing, lap length, and bar weight.
Results
- Bars running length
- 21.00
- Bars running width
- 31.00
- Total linear feet
- 1354.00 ft
- Estimated weight
- 904.47 lb
How to use this calculator
- Enter slab length/width in feet.
- Enter spacing in inches for each direction, lap length, and bar weight per foot.
- We compute bar counts each way, total linear feet, and estimated weight.
Inputs explained
- Slab length/width
- Overall slab dimensions in feet.
- Spacing across width/length
- Center-to-center spacing in inches for bars running the opposite direction.
- Lap/overlap
- Extra length per bar for overlaps/hooks in feet.
- Bar weight per foot
- Weight per linear foot (e.g., #4 ≈ 0.668 lb/ft). Adjust for bar size.
How it works
We convert slab width/length to inches and divide by spacing to count how many bars are needed in each direction (always rounding up and adding one).
Lap length accounts for overlaps or hooks, so we add it to each bar’s length.
Total weight = linear feet × weight per foot, letting you approximate bundle weights or delivery loads.
Formula
Bars‖length = ⌊(width × 12) ÷ spacing_width⌋ + 1 Bars‖width = ⌊(length × 12) ÷ spacing_length⌋ + 1 Linear ft = Bars‖length × (length + lap) + Bars‖width × (width + lap) Weight = Linear ft × weight/ft
When to use it
- Estimating rebar quantities for slabs or pads before ordering.
- Comparing spacing scenarios (12 in vs 18 in) and their impact on bar count/weight.
- Planning delivery weights for handling or transport.
Tips & cautions
- Confirm spacing and lap lengths with your engineer; this tool is for planning only.
- Increase lap length for larger bar sizes per code/engineer requirements.
- If two layers are required, run the calculation twice or double the totals.
- Planning aid only—follow engineered drawings and code.
- Assumes uniform spacing and rectangular slabs.
- Weight uses a single bar weight input; actual weight varies slightly by manufacturer.
Worked examples
Garage pad with 18 in spacing
- Increase spacing to reduce bar count but confirm with your engineer first.
Deep dive
This rebar calculator counts bars, linear footage, and weight for slab grids. Enter slab dimensions, spacing, lap length, and bar weight to size a rebar order quickly.
Use it to compare spacing scenarios or plan delivery weights. Always follow engineered plans and code for final layouts.
FAQs
- Can I include two layers?
- Run the calculator twice (one for each layer) and add the totals, or double the results manually.
- Is spacing center-to-center?
- Yes. Standard practice is to specify center spacing in inches.
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Always follow engineered plans and local code requirements. This tool is a planning aid, not a structural design.