Rebar Calculator
Example: Slab length: 20 ft · Slab width: 12 ft · Grid spacing (on center): 12 in · Stock bar length: 20 ft
| Total rebar length | 512 |
| Stock bars to buy | 26 |
| Grid intersections (ties) | 273 |
Worked example
A 20 by 12 foot slab with rebar at 12 inches on center each way needs bars running the length spaced across the 12-foot width (13 bars x 20 ft = 260 ft) plus bars running the width spaced across the 20-foot length (21 bars x 12 ft = 252 ft), for 512 linear feet of steel. In 20-foot stock bars that is 26 bars, and the grid has about 273 intersections to tie.
Frequently asked questions
What rebar spacing should I use?
Spacing is set by the structural design and the slab's load, commonly 12 to 18 inches on center each way for residential slabs, sometimes tighter for heavier loads. The bar size and spacing come from an engineer or a code table for your application, so enter the specified spacing rather than guessing.
Do I need to add for lap splices?
Yes, where bars overlap end to end they must lap by a code-specified length, often around 40 bar diameters, which consumes extra steel on long runs. This tool counts the grid length; add a percentage for laps on any dimension longer than your stock bar, plus bar to spare.
What are the grid intersections for?
Each place where a length bar crosses a width bar is tied with wire to hold the mat together during the pour. The intersection count estimates how many ties and roughly how much tie wire you need, and hints at the labor to assemble the mat.
Can I use welded wire mesh instead?
For many light residential slabs, welded wire reinforcement in sheets or rolls is an alternative to a tied rebar grid and is faster to place. If you go that route, size it by area and overlap instead of using this bar-grid tool, which is aimed at rebar reinforcement.