Calculate rebar bar count, total linear feet, and estimated weight for concrete slabs and continuous footings. Enter your slab dimensions and spacing to get a full material takeoff.
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Shop Express Tools →Rebar count per direction = (Slab dimension ÷ spacing) + 1. Total linear feet = bars in each direction × their run length, summed for both directions. Standard residential slab: #4 rebar at 12" OC each way. A 20×20 ft slab at 12" OC needs 21 bars each way × 20 ft = 840 LF total.
Rebar (reinforcing bar) gives concrete its tensile strength. Concrete is strong in compression but weak in tension — rebar bridges that gap. The spacing determines how much steel is in the slab per unit area, which directly affects the slab’s ability to resist cracking and distribute loads. The formula:
| Bar Size | Diameter | Weight (lbs/LF) | Common Use |
|---|---|---|---|
| #3 | 3/8" | 0.376 lb/ft | Light slabs, slab-on-grade tie |
| #4 | 1/2" | 0.668 lb/ft | Standard residential slabs and footings |
| #5 | 5/8" | 1.043 lb/ft | Structural slabs, commercial footings |
| #6 | 3/4" | 1.502 lb/ft | Heavy slabs, retaining walls |
| #7 | 7/8" | 2.044 lb/ft | Structural beams, columns |
| #8 | 1" | 2.670 lb/ft | Heavy structural members |
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Start free trialMost residential concrete slabs use #4 rebar at 12" on center in both directions. Heavier loads or thicker slabs may require 8" or 6" spacing. Always follow engineer specifications for structural slabs.
Divide the slab width by the spacing (converted to feet) and add 1 for the number of bars in each direction. Multiply by the length to get total linear feet. For example, a 20×10 ft slab at 12" spacing needs (10÷1)+1 = 11 bars × 20 ft = 220 LF in one direction.
#3 rebar weighs 0.376 lb/ft, #4 rebar weighs 0.668 lb/ft, #5 rebar weighs 1.043 lb/ft, and #6 rebar weighs 1.502 lb/ft. This calculator estimates weight based on #4 rebar — adjust for other sizes.
ACI 318 requires a minimum of 3/4" cover for concrete cast against and permanently exposed to earth. Slabs not exposed to weather typically require 3/4" to 1.5" cover. Check your local code and engineer drawings.
Rebar bundles vary by size. #4 rebar (1/2") is often sold in 20-foot lengths and bundled in quantities of 30–40 bars. Most suppliers sell by the ton or by linear feet — use this calculator to determine your total linear footage and then order accordingly.
Weight estimate based on #4 rebar (0.668 lb/ft). Adjust for other sizes.