Rebar Calculator
Calculate rebar needed for concrete slabs, footings, and walls
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Quick Answer
For a 20×20 slab with 12" spacing, you need approximately 42 bars of rebar running both directions.
Reinforcing bar (rebar) strengthens concrete by adding tensile strength. This calculator helps you determine the amount of rebar needed for slabs, footings, walls, and other concrete projects based on area dimensions and desired spacing.
Dr. Snezana Lawrence
Mathematical Historian
15+ years experience
PhD from Yale University. Published mathematical historian ensuring precision in all calculations.
Education
PhD in Mathematical History - Yale University
Rebar Size Reference
| Size | Diameter | Weight (lbs/ft) |
|---|---|---|
| #3 | 3/8" (10mm) | 0.376 |
| #4 | 1/2" (13mm) | 0.668 |
| #5 | 5/8" (16mm) | 1.043 |
| #6 | 3/4" (19mm) | 1.502 |
| #7 | 7/8" (22mm) | 2.044 |
| #8 | 1" (25mm) | 2.67 |
Spacing Guidelines
- • 12" on center - Standard for residential slabs
- • 18" on center - Light-duty applications
- • 6" on center - Heavy-duty or structural applications
- • Always maintain 3" cover from concrete edges
- • Overlap bars by 40 bar diameters at splices
Frequently Asked Questions
What size rebar for a 4" slab?
#3 or #4 rebar is standard for 4" residential slabs with 12" spacing.
Do I need rebar for a patio?
Yes, rebar or wire mesh is recommended for patios to prevent cracking. Use #3 or #4 rebar at 18" spacing.
Dr. Snezana Lawrence
Mathematical Historian | PhD from Yale
Dr. Lawrence is a published mathematical historian with a PhD from Yale University. She ensures mathematical precision and accuracy in all our calculations, conversions, and academic score calculators. Her expertise spans computational mathematics and educational assessment.
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