Rebar Calculator

12 inches on center for residential slabs like driveways and patios. Sidewalks and small pads sometimes go out to 18-24 inches. Those are conventions, not rules: local code or an engineer's spec beats both, and on anything structural that is the number to build to.

Bars in one direction get spaced across the slab's other dimension, plus one extra so both edges are bracketed. That plus-one is the step people forget, and it is why a hand count usually comes out one bar short per direction. The calculator does both directions and totals the linear footage.

20 ft and 40 ft sticks are the standard stock lengths, sold full or cut in half. Set the stick length field to whatever your supplier actually carries, since that determines how many you buy and how much you end up cutting off.

Yes. Bars that meet have to overlap in a lap splice, not butt end to end, typically 12-18 inches depending on code and bar size. Add roughly 10% to the linear footage above to cover the laps and the offcuts.

Yes. Bar size changes weight and strength, not geometry, so a #3 grid and a #5 grid at the same spacing need the same number of bars and the same linear footage. Only the tonnage and the price change.