How Much Rebar for a 40x20 ft Driveway Slab?
A 40×20 ft driveway slab with rebar on 18-inch centers using 20-foot bars requires approximately 54 bars.
How to use this tool
- Enter the slab dimensions in feet.
- Set the rebar spacing (12 inches is standard for residential slabs).
- Enter the standard bar length you'll purchase (typically 20 ft).
- The result shows total linear footage and number of bars to buy.
Calculate how many rebar bars are needed to reinforce a 40×20 foot concrete driveway slab with 18-inch spacing.
Frequently asked questions
- How much rebar do I need for a slab?
- For a standard grid pattern with 12-inch spacing, calculate both directions of bars, multiply by the slab dimension in each direction, then add them together.
- What rebar size for a concrete slab?
- #3 rebar (3/8-inch diameter) is standard for residential slabs 4 inches thick. Use #4 (1/2-inch) for 5–6 inch driveways or higher-load applications.