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Calculate rebar needed for concrete slabs. Get bar count, linear feet, and weight with independent X and Y spacing.
Enter the length and width of your concrete slab in feet. For irregular shapes, calculate rebar for each rectangular section separately and add the totals.
Choose the appropriate bar size based on slab thickness and load requirements. #4 (1/2 inch) is standard for most residential slabs. The calculator shows weight per foot for each size.
Standard spacing is 12 inches on center in both directions. Use 6 inches for heavy loads (driveways, equipment pads) or 18 inches for lighter applications. Spacing can be set independently for each direction.
The default 10% waste factor accounts for cuts, overlaps, and unusable pieces. Increase to 15% for complex shapes or if bars must be cut from standard 20-foot lengths.
The calculator shows bars needed in each direction, individual bar lengths, total linear feet, and total weight. Use linear feet for ordering cut-to-length rebar, or weight for bulk purchases.
| Size | Diameter | Weight/ft | Typical Use |
|---|---|---|---|
| #3 | 3/8" | 0.376 lb | Thin slabs, temperature steel |
| #4 | 1/2" | 0.668 lb | Residential slabs, driveways |
| #5 | 5/8" | 1.043 lb | Heavy loads, commercial |
| #6 | 3/4" | 1.502 lb | Structural, heavy commercial |
| #7 | 7/8" | 2.044 lb | Foundations, columns |
| #8 | 1" | 2.670 lb | Heavy structural |
Length of the concrete slab
Width of the concrete slab
#4 is standard for residential slabs, #5 for heavy loads
Common: 6", 12", 18" on center
Common: 6", 12", 18" on center
Accounts for cuts, overlaps, and waste
9.5 ft each
9.5 ft each
With waste factor
#4 (1/2 in) rebar
10 running length + 10 running width
Standard spacing is 12" on center. Use 6" for heavy loads (driveways, equipment pads), 18" for lighter applications (patios, walkways).