Calculator

Slab length (ft)

Slab width (ft)

Bar spacing (in, on-center)

Bar size

Waste / laps (%)

Price per lb ($)

Total Weight (lb)

Total Length (ft)

Weight (kg)

Bars (length direction)

Bars (width direction)

Estimated Material Cost

Builds a two-way reinforcement grid: bars running the slab's length are spaced across its width, and bars running its width are spaced across its length. Weight-per-foot values follow the standard ASTM A615 rebar size table. Spacing is a design decision — confirm it against your engineer's drawings.

Enter a slab's dimensions, bar spacing, and bar size to calculate total rebar length, weight, and cost.

A slab's reinforcement isn't a handful of loose bars — it's a grid, with bars running both directions at a set spacing, and this calculator builds that grid from the slab's dimensions rather than asking for a bar count you'd have to work out by hand first.

How to Use the Rebar Material Calculator

Enter the slab's length and width, a bar spacing (on-center, in inches), and a bar size. Total length, weight, and cost update together, alongside the bar count in each direction.

bars across width = ⌊(width × 12 ÷ spacing)⌋ + 1
bars across length = ⌊(length × 12 ÷ spacing)⌋ + 1
total length = (bars across width × length + bars across length × width) × (1 + waste %)
weight = total length × weight per foot (from bar size)

Bar spacing is a structural design choice, not a physical constant — 12 in. on-center is a common default for light residential slabs, but an engineer's drawings might call for 8, 16, or 18 in. depending on the load. Change the spacing field to match whatever the actual plans specify rather than trusting the default on anything structural.

The rebar-per-foot weights themselves aren't a guess: they're the standard ASTM A615 bar sizes, the same table stamped on mill certificates industry-wide.