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Rebar Calculator

Estimate rebar quantity, length, weight & material list for slabs, walls & footings

Enter the slab, wall or footing size and it returns bar count, total length, lap allowance, weight and a cost estimate. A 20 ft × 20 ft slab in #4 at 12 in on centre both ways is 40 bars, 800 ft, 534.4 lb.
0.668 lb/ft#4, the default bar
40bars in 20 × 20 ft at 12 in
534.4 lbthat slab, both ways
1.3Class B lap multiplier

No account and no upload — the arithmetic runs in your browser. Cover, lap class and waste are inputs, not hidden assumptions.

Inputs

ft
ft
in
in
in
$ / bar

Results

Where to Buy Rebar

Once you have your bar sizes, lengths and piece counts, the next step is buying. eBay lists rebar, rebar ties, wire mesh and bar cutters from many sellers, so you can compare price per piece before you order.

Affiliate disclosure: the links below are affiliate links. If you buy through them, we may earn a commission at no extra cost to you, and it does not change the price you pay.
Shop rebar on eBay → Opens eBay in a new tab
Also on eBay: Rebar ties Wire mesh Bar cutters

Formulas Used

Grid Length = Length − 2 × Edge Clearance
Grid Width = Width − 2 × Edge Clearance
Bars (Dir 1) = ⌊ Grid Width / Spacing ⌋ + 1
Bars (Dir 2) = ⌊ Grid Length / Spacing ⌋ + 1
Total Length = Σ(Bars × Bar Length) + Lap Allowance
Lap Allowance = Lap Length × (Pieces per Bar − 1) × Bars (when bar > standard length)
Weight (lb/ft) = (π × d² × 490) / 576   d = diameter in inches, 490 = steel density (lb/ft³)
Total Weight = Total Length × Unit Weight
Weight to Order = Pieces × Standard Bar Length × Unit Weight
Pieces = Σ⌈ Bar Length / Standard Bar Length ⌉ × Bars

Lap length defaults to 40 × bar diameter (common practice). Override with your own value if needed. Total Weight is the steel in the finished work, laps included. Weight to Order counts whole stock bars, so it includes offcut waste — use that figure when buying by weight. Results are for material estimation only. Always follow your project's engineering specifications. Not sure which bar size to pick? See the rebar size & weight chart. Weighing bar against welded wire mesh? See rebar vs wire mesh.