Rebar Calculator
Calculate the rebar grid for a concrete slab — bars each direction, total linear feet, and how many 20 ft sticks to buy.
Total linear feet
635ft
Sticks to buy
32sticks
Bars one way
16bars
Bars other way
21bars
Add about 10% extra linear footage for lap splices at bar overlaps and cutting waste — this figure is the raw grid length only.
How the rebar calculator works
Slab rebar is laid out as a grid: bars run in both directions at a fixed spacing. The number of bars running lengthwise depends on how many fit across the slab's width (and vice versa), with one extra bar added so both edges are covered.
Formula: bars one way = (width ÷ spacing) + 1. Bars the other way = (length ÷ spacing) + 1. Total linear feet = (bars one way × length) + (bars other way × width).
Frequently asked questions
12 inches on-center is the standard grid spacing for residential slabs like driveways and patios. Lighter-duty pours (sidewalks, small pads) sometimes use 18-24 inch spacing instead — check your local code or engineer's spec.
Bars running in one direction are spaced out across the slab's other dimension, plus one extra bar to bracket both edges. This calculator works out both directions and adds up the total linear footage.
Standard stock lengths are 20 ft and 40 ft sticks (sold as full or half sticks). Set the stick length field to whatever your supplier carries to see how many sticks to order.
Yes — where two bars meet, they need to overlap (lap splice) rather than butt together, which is typically 12-18 inches per code. Add roughly 10% to the calculated linear footage to cover laps and cut waste.
Yes — the linear-footage grid math is the same regardless of bar size (#3, #4, #5, etc.). Bar size affects weight and strength, not how many bars fit in the grid, so this calculator works for whichever size your project calls for.