Rebar Calculator
Rebar in a slab goes down in a grid, and the count depends on your spacing and edge clearance, not just the slab size. Enter your slab's length and width and your grid spacing below. The calculator returns how many bars run each direction, the total linear feet to order, and a cost estimate, so you can buy the right number of sticks the first time.
How this is calculated
For each direction, take the slab dimension, subtract clearance from both edges (usually about 3 inches), divide by your bar spacing, and add one, that's the number of bars running that way. Multiply each count by the length those bars span, add the two directions together, and you have total linear feet. Rebar is sold in fixed lengths (commonly 20 feet), so the tool also tells you how many sticks that works out to.
A worked example
A 20 by 30 foot slab with 12-inch grid spacing and 3-inch edge clearance: bars one way span 30 feet and you'll have about 20 of them; bars the other way span 20 feet with about 30 of them. That's 600 plus 600, roughly 1,200 linear feet. At 20 feet per stick, you're ordering about 60 sticks. The calculator handles both directions at once.
Common questions
It depends on slab size and grid spacing. Enter both above and the calculator gives bar counts each way and total linear feet. Tighter spacing means more steel; 12 to 18 inches is common for residential slabs.
Twelve to eighteen inches on center covers most residential slabs and footings, but follow your engineer or local code for anything structural. The tool lets you set whatever spacing your plan calls for.
Commonly 20 feet, though 10 and 40 foot lengths exist. The calculator converts your total linear feet into stick count so ordering is simple.
For driveways, footings, and anything bearing load, yes, it controls cracking and adds tensile strength. Thin decorative slabs sometimes use wire mesh instead. Check your local requirements.
Estimates for planning. Verify against your supplier's units and your local building codes before ordering or building. For anything structural, follow your engineer or local code.