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Rebar Calculator
Enter your slab length, width, and rebar spacing to get the number of bars in each direction, total linear feet, and the count of standard 20 ft sticks to buy.
Change any measurement to update your estimate.
- Bars lengthwise
- 10
- Bars widthwise
- 10
- 20 ft sticks to buy
- 10
Field notes
The edge clearance matters more than people expect — rebar needs about 3 inches of concrete cover from any face, or it rusts and spalls the slab from the inside. That's why the calculator trims the grid in from the edges. Buy your bar in 20 ft sticks and cut on site rather than ordering odd lengths; a rebar bender and cutter rents for less than the premium on pre-cut bar.
How the rebar calculator works
The math behind the tool:
bars along a side = floor(side length ÷ spacing) + 1
total length = bars_x × width + bars_y × lengthSources: Portland Cement Association (concrete density and mix guidance).
Frequently asked questions
How do you calculate rebar for a slab?
Divide each slab dimension by the bar spacing and add one to get the bar count in that direction, then multiply by the opposite dimension for total length. A 10 × 10 ft slab at 12-inch spacing uses about 22 bars and 220 linear feet.
What spacing should rebar be in a concrete slab?
Residential slabs commonly use #3 or #4 rebar on a 12-to-18-inch grid; check your local code and engineer for load-bearing slabs.
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Step-by-step guides
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