Rebar Calculator
Lay out a rebar grid for a slab: bar count each way, total length, stock bars to buy and weight.
Stock bars to buy
43 × 20 ft
- Bars each way
- 20 lengthwise × 20 crosswise
- Total bar length
- 780 ft
- Weight of bars bought
- 574.48 lb (260.6 kg)
- Bar weight
- 0.668 lb/ft
Lap splices and chairs aren't included — use the lap length your engineer or local code calls for. Material counts are estimates — check with your supplier and local code before you buy.
Show the work
Bar runs: each side in inches, minus the cover at both ends
run = side × 12 − 2 × cover
20 × 12 − 2 × 3; 20 × 12 − 2 × 3 = 234 in; 234 in
Bars each way: run across ÷ spacing, rounded down, plus 1
bars = ⌊run across ÷ spacing⌋ + 1
⌊234 ÷ 12⌋ + 1; ⌊234 ÷ 12⌋ + 1 = 20 lengthwise; 20 crosswise
Total bar length in feet
total = (lengthwise × run + crosswise × run) ÷ 12
(20 × 234 + 20 × 234) ÷ 12 = 780 ft
Stock bars to buy (count × bar length), plus waste, rounded up
bars = ⌈total × (1 + waste ÷ 100) ÷ stock length⌉
⌈780 × (1 + 10 ÷ 100) ÷ 20⌉ = 43 × 20 ft
How it works
Bars each way = ⌊(slab side − 2 × cover) ÷ spacing⌋ + 1; total length = bars × bar length (both ways); weight = length × lb/ft (ASTM A615)
Questions
- How does the rebar calculator work?
- Bars each way = ⌊(slab side − 2 × cover) ÷ spacing⌋ + 1; total length = bars × bar length (both ways); weight = length × lb/ft (ASTM A615).
- What do I need to enter?
- Slab length, Slab width, Grid spacing, Edge cover, Bar size, Stock bar length, Extra for waste. Optional fields can be left blank.
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