Rebar Calculator
Calculate how much rebar you need for concrete slabs, driveways, and foundations. Get accurate rebar quantity, spacing, weight, and cost estimates.
Last updated: January 15, 2026
Enter Your Measurements
Automatically sets recommended rebar size and spacing
Based on ASTM A615 standards
Distance between rebar bars (center to center)
Affects minimum concrete cover per ACI 318-19
Results
Area:200 sq ft (18.58 m²)
Total Rebar:23 pieces
Buy at store: 16 × 20ft bars
Length direction:15 pieces
Width direction:8 pieces
Linear Feet:304.25 ft (92.74 m)
Total Weight:203.24 lbs (92.19 kg)
Min. Cover:1.5"
Rebar should be placed in the lower third of the slab for maximum tensile strength.
How to Use This Calculator
- Select your project type - Choose from driveway, patio, foundation, or custom. This automatically sets recommended rebar size and spacing.
- Enter area dimensions - Measure your slab length and width in feet. For circular slabs, enter the diameter.
- Choose rebar size - #3 or #4 for residential slabs, #4 or #5 for driveways and foundations. The calculator shows weight per foot for each size.
- Set spacing - Standard spacing is 12-18 inches on center. Per ACI 318, maximum spacing is 3× slab thickness or 18", whichever is smaller.
- Select exposure condition - This determines the minimum concrete cover required to protect the rebar from corrosion.
How We Calculate
Rebar Count (each direction) = (Dimension ÷ Spacing) + 1
Total Linear Feet = Count × (Perpendicular Dimension - 2 × Cover)
Total Weight = Linear Feet × Weight per Foot
Example Calculation:
- • Slab: 20 ft × 10 ft = 200 sq ft
- • Rebar: #4 (0.668 lb/ft)
- • Spacing: 18" (1.5 ft) on center
- • Cover: 1.5" (outdoor exposure)
- • Length direction: 20 ÷ 1.5 + 1 = 14 bars
- • Width direction: 10 ÷ 1.5 + 1 = 8 bars
- • Total: 14 + 8 = 22 bars
- • Linear feet: (14 × 9.75) + (8 × 19.75) = 294.5 ft
- • Weight: 294.5 × 0.668 = 197 lbs
Rebar spacing and cover requirements per ACI 318-19 standards. Rebar specifications per ASTM A615. Learn more about ACI standards