How Much Rebar Do You Need?
Turn slab, driveway, patio, or footing dimensions into 20-ft bars, total linear feet, weight, and a clear rebar buy list.
Last updated: May 9, 2026
Build Your Rebar Order
Start with the project type and size. The calculator applies a common rebar size and spacing unless you open Advanced settings.
#3 or #4 rebar at 18" grid for residential driveways
Rebar Order Summary
Assumptions: 20 x 10 ft rectangle, #4, 18" spacing, two-way grid, outdoor (exposed to weather), 1.5" minimum cover.
Project Examples
Driveway Slab
20 ft × 10 ft slab · #4 rebar · 18 in spacing
A small driveway slab usually lands around 15 standard 20 ft bars once you convert the grid into total linear feet.
Patio Slab
12 ft × 12 ft slab · #3 rebar · 18 in spacing
A patio layout stays lighter, but the order still rounds up fast because store stock lengths are usually sold in 20 ft bars.
Garage Floor
24 ft × 24 ft slab · #4 rebar · 16 in spacing
Larger garage floors push both bar count and weight quickly, so it helps to estimate stock lengths before calling a supplier.
Rebar Size Guide
Spacing Guide
20-ft Bar Buying Guide
Start with stock lengths
Most retail orders are easier to think about as 20-ft sticks. The calculator rounds your total linear feet up to whole 20-ft bars.
Leave room for cuts and laps
Complex shapes, overlaps, and field cuts can need extra material beyond a clean grid estimate. Add a small buffer if the layout is not simple.
Confirm placement before the pour
Rebar should stay in the lower third of the slab with proper cover, chairs, or supports so it does not end up at the bottom.
Wire Mesh vs Rebar
For structural slabs, driveways, and footings, use local code or a qualified professional to confirm the final reinforcement design.