Calculate how much rebar you need for concrete slabs, footings, and walls. Get results in number of bars, total linear feet, and weight based on rebar size and spacing.
Estimates only — always follow structural engineer specifications for load-bearing concrete.
Reinforcing a 10×10 foot slab with #4 rebar at 12-inch spacing in both directions? You need 11 bars each way — 22 bars total, 220 linear feet. At 0.668 lbs per foot, that's about 147 pounds of rebar. At standard 20-foot stock lengths, you need 11 sticks of rebar.
| Rebar Size | Diameter | Weight/Foot | Weight/20-ft Bar |
|---|---|---|---|
| #3 | 3/8" | 0.376 lbs | 7.5 lbs |
| #4 | 1/2" | 0.668 lbs | 13.4 lbs |
| #5 | 5/8" | 1.043 lbs | 20.9 lbs |
| #6 | 3/4" | 1.502 lbs | 30.0 lbs |
| #7 | 7/8" | 2.044 lbs | 40.9 lbs |
| #8 | 1" | 2.670 lbs | 53.4 lbs |
# 4 rebar (1/2 inch) is standard for most residential slabs — patios, driveways, sidewalks. Use #5 for garage floors and any slab supporting heavy loads.
12 inches on-center in both directions is standard for 4-inch residential slabs. 18-inch spacing is acceptable for lightly loaded slabs. Use 6-inch spacing for heavy-duty applications.
At 12-inch spacing in both directions, approximately 2 linear feet of rebar per square foot. At 18-inch spacing, about 1.3 feet per square foot.
For patios and walkways with no vehicle traffic, wire mesh or fiber reinforcement is often sufficient. For driveways, garage floors, or any slab that may crack under load, rebar is strongly recommended.
#4 rebar runs about $0.50–$0.80 per linear foot at most suppliers. A 20-foot stick costs $10–$16. Prices vary by region and steel market conditions.
Typical Results
💡 If bar count seems too high, check your spacing is in inches — entering 1 instead of 12 gives 12× more bars than a 12" grid.
Common Mistakes