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Rebar Calculator
Calculate rebar bars, ties, and weight for a concrete slab grid. Get bar count, stock bars to order, tie wires, and total linear feet at any spacing.
Slab and rebar grid
Stock bars to order
44 bars
#4 rebar, 20 ft each
- Bars lengthwise
- 20 bars
- Bars widthwise
- 20 bars
- Total linear feet
- 800 ft
- Total linear meters
- 243.84 m
- With waste
- 880 ft
- Tie wires (intersections)
- 400
- Weight per linear foot
- 0.668 lb/ft
- Total weight
- 587.8 lb
Frequently Asked Questions about the Rebar Calculator
What grid spacing should I use for a residential slab?
For most residential concrete slabs, 12 in on center with #4 rebar is the standard. Drop to 18 in on center for lightly loaded slabs like patios, or tighten to 6 in for driveways that see truck traffic.
Which rebar size do I need?
#3 is fine for sidewalks and small patios. #4 is the workhorse for residential slabs, driveways, and footings. #5 is used for heavily loaded slabs and retaining walls. #6 is reserved for columns, large footings, and commercial work.
How is the bar count calculated?
For each axis, subtract twice the edge offset from the slab dimension, divide by grid spacing, take floor, and add one. For a 240 in slab with 3 in offset and 12 in grid, that is floor((240 - 6) / 12) + 1 = 20 bars.
Why does the calculator add 10% waste?
Real layouts need lap splices wherever bars meet, plus extra length bent into footings, hooks at slab edges, and a few cuts that don't reuse. 10% covers a simple rectangular slab. Bump to 15% for many splices or many penetrations.
What is the tie wire count, and do I need to order extra?
It is the number of grid intersections, which equals bars-lengthwise times bars-widthwise. A 3.5 lb roll of 16-gauge tie wire ties roughly 1,000-1,500 intersections, so one roll handles most residential slabs comfortably.