Rebar Grid Calculator

How to Use the Rebar Grid Calculator

Enter your slab's length and width in feet, plus the grid spacing you're using in inches (commonly 12", 16", or 18" for residential slabs). The calculator lays out a two-way grid of rebar running both directions and tells you the total linear footage of steel and how many 20 ft sticks to order.

How the Calculation Works

Rebar grids run perpendicular to each other, at right angles. The calculator finds how many bars are needed running in each direction by dividing the opposite dimension by your spacing and adding one bar to cover both edges. It then multiplies each set of bars by their length, sums the two totals for the total linear footage, and divides by 20 (the standard stock length for rebar) to get the number of full sticks to buy.

Example Calculation

For a 20×20 ft slab at 18-inch (1.5 ft) spacing: rows running length-wise = floor(20 ÷ 1.5) + 1 = 14, and rows running width-wise = floor(20 ÷ 1.5) + 1 = 14. Total linear footage = (14 × 20) + (14 × 20) = 560 ft. At 20 ft per stick, that's 560 ÷ 20 = 28 sticks.

Frequently Asked Questions

Does this account for overlap at splices?

No — this is a straight linear-footage estimate. If your bars need to be spliced together (common on larger slabs where a single 20 ft stick doesn't reach), add roughly 12–18 inches of overlap per splice, per typical rebar lap-splice guidance and your local code.

What rebar spacing should I use?

18 inches on-center is common for residential slabs and patios. Heavier-duty slabs like driveways or shop floors often use 12–16 inch spacing with thicker bar for added strength — check your project's engineering spec or local code.

Do I need rebar for every concrete pour?

Not always — thin slabs like a small walkway are sometimes poured with just wire mesh or no reinforcement at all. Rebar matters most for slabs that bear structural loads, span unstable soil, or are subject to freeze-thaw cracking.