Rebar Calculator
Get bar counts, total length, and how many 20-foot sticks to buy for any slab grid.
length = 10×11.5 + 12×9.5 = 229 lf → sticks = ceil(229 ÷ 20) = 12
Rebar in a slab is laid as a grid at a fixed spacing, held back from every edge by the concrete cover. The number of bars in one direction is the clear span divided by the spacing, plus one — the plus-one is the bar at the far edge that the division alone misses.
Each bar spans the clear dimension of the slab, edge cover subtracted from both sides. Add up the length of every bar in both directions to get total linear feet, then divide by the stock length — 20 ft is the common stick — and round up to know how many to buy.
Bars overlap at splices where a run is longer than a single stick; a common lap is 40 times the bar diameter. This estimate counts the grid length only, so add a bit for laps on large slabs.
bars along 12′ side = floor((120 − 6) ÷ 12) + 1 = 10, each 11′6″
bars along 10′ side = floor((144 − 6) ÷ 12) + 1 = 12, each 9′6″
total = 10 × 11.5 + 12 × 9.5 = 229 lf → sticks = ceil(229 ÷ 20) = 12