Rebar Calculator
Enter your slab dimensions and grid spacing to estimate the number of rebar bars in each direction, the total linear feet, and the number of grid intersections to tie.
Results
- Total rebar length
- 269.5 ft
- Bars (lengthwise)
- 7 × 19.5 ft
- Bars (widthwise)
- 14 × 9.5 ft
- Tie intersections
- 98
Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.
This calculator lays out a rebar grid for your slab or footing and returns bar counts in each direction, total linear feet, and the number of tie intersections.
Rebar controls cracking, it does not prevent it. Correct spacing and correct placement in the middle third of the slab matter more than bar size.
Also works as a rebar grid calculator, slab reinforcement calculator, and rebar tie estimator.
How to use the rebar calculator
- Enter the slab length in ft.
- Enter the slab width in ft.
- Enter the grid spacing in in.
- Enter the edge clearance in in.
- Optionally add a price to estimate the total project cost.
- Read your quantities instantly — no sign-up, and you can print the estimate to take to the supplier.
Worked example
Inputs
- Slab length
- 20 ft
- Slab width
- 10 ft
- Grid spacing
- 18 in
- Edge clearance
- 3 in
Results
- Total rebar length
- 269.5 ft
- Bars (lengthwise)
- 7 × 19.5 ft
- Bars (widthwise)
- 14 × 9.5 ft
- Tie intersections
- 98
Using the example values above, the rebar calculator returns 269.5 ft (total rebar length). Change any field to match your own project and the numbers update instantly.
Typical spacing and sizes
Residential slabs and patios: #3 or #4 bar on 18 inch centers. Driveways and garage slabs: #4 bar on 12 to 16 inch centers. Footings: two runs of #4 continuous.
Keep 3 inches of cover from soil and 1.5 inches from formed edges so the steel does not rust and spall the concrete.
Ordering and overlap
Rebar comes in 20 ft sticks. Lap splices should be at least 40 bar diameters, which is 20 inches for #4 bar, and every lap adds to your total footage.
Add about 10 percent to linear footage for laps and offcuts, and figure roughly one tie wire per intersection at 4 to 6 inches per tie.
Formula
Bars = (dimension ÷ spacing) + 1 in each direction. Total length = bars × run length. Intersections = bars across × bars down.
Frequently asked questions
- What spacing should rebar be in a slab?
- Residential slabs typically use #3 or #4 rebar on a 16–18 inch grid; driveways and heavier loads use 12 inch spacing.
- How much rebar do I need for a concrete slab?
- Lay a grid both directions: add 1 bar to (each dimension ÷ spacing), multiply by the run length, and sum both directions for total linear feet.
- How far should rebar be from the edge?
- Keep rebar about 3 inches from each edge and roughly centered in the slab thickness so concrete fully encases it.
- How much rebar for a 20 by 20 slab?
- On 18 inch centers you need about 14 bars each way at 20 ft, roughly 560 linear feet plus 10 percent for laps.
- What size rebar for a driveway?
- #4 bar (1/2 inch) on 12 to 16 inch centers is standard for residential driveways carrying vehicle loads.
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