Rebar Calculator
Free rebar calculator. Enter slab size, bar spacing and size to get the number of rebar pieces, linear feet, weight in pounds, and ties for a reinforced concrete slab.
About This Free Online Rebar Calculator
Our free rebar calculator works out how much reinforcing steel you need for a concrete slab or footing. Enter the slab length and width, the on-center bar spacing, and the rebar size (#3 to #8), and the tool returns the number of bars in each direction, the total bar count, the linear feet, the weight in pounds, and the number of wire ties. A lap option adds 10% for overlapping splices. Everything runs in your browser — perfect for concrete contractors and DIYers.
Features of Our Rebar Calculator
- Bar count in each direction from slab size and spacing
- Total linear feet of rebar
- Weight in pounds by rebar size (#3 to #8)
- Optional lap allowance for spliced bars
- Wire tie count for the intersections
- 100% client-side and private — instant results, no signup
How to Use the Rebar Calculator
Using this tool is simple and requires no signup or registration. Follow these steps:
- Enter the slab length and width in feet.
- Set the on-center rebar spacing (commonly 16 or 24 in).
- Pick the rebar size and tick lap if you are splicing.
- Read off bar count, linear feet, weight and ties.
Frequently Asked Questions About Rebar Calculator
How much rebar do I need for a slab?
Divide each slab dimension by the spacing to get the bar count in each direction, then add one bar and multiply by the length. For example, a 20×20 ft slab at 16 in spacing needs about 16 bars each way. The calculator does the count, linear feet and weight for you.
What size rebar should I use?
#3 (3/8 in) suits light slabs and walkways, #4 (1/2 in) is the most common for residential driveways and floors, and #5 (5/8 in) or larger suits heavier slabs and foundations. The weight per foot changes with size — the calculator applies it automatically.
How far apart should rebar be spaced?
Rebar is typically spaced 12, 16 or 24 inches on center in a grid pattern. Closer spacing means stronger reinforcement. For a 4 in residential slab, 16 or 24 in on center is common.
How much rebar weighs?
Rebar weight per foot depends on size: #4 is about 0.668 lb/ft, #5 is 1.043 lb/ft. Multiply the linear feet by the per-foot weight for your size to get the total pounds. The calculator does this and can include lap splice allowance.
Is this rebar calculator free?
Yes, completely free with no signup. All maths runs in your browser — nothing is uploaded or tracked.
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