Rebar Calculator
Calculate rebar quantity, spacing, and total length needed for concrete slabs, footings, and walls.
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How to Calculate Rebar for a Slab
Count bars in each direction: divide slab dimension by spacing and add 1. Multiply bars by length to get total linear feet. Add 10% for overlap at splices.
Frequently Asked Questions
What size rebar do I need?
#3 (3/8") for patios and walkways. #4 (1/2") for driveways and residential footings. #5 (5/8") for structural slabs and retaining walls.
What is standard rebar spacing?
12 inches on center for driveways, 18 inches for patios, and 24 inches for light-duty slabs.
How much does rebar cost?
#3 (10mm): $3-$5 per 20 ft bar. #4 (12mm): $5-$8 per 20 ft bar. #5 (16mm): $8-$12 per 20 ft bar. Bulk pricing is 10-20% cheaper. Wire ties cost about $5-$10 per 200-count box.
Do I need rebar in a concrete slab?
Rebar is recommended for any slab over 100 mm (4 in) thick that will bear loads. Patios and walkways can use wire mesh instead. Driveways, garage floors, and any slab on fill or clay soil should have rebar at minimum 12-inch spacing.
How much overlap do rebar splices need?
Minimum lap splice is 40 bar diameters. For #4 rebar: 40 x 1/2 inch = 20 inches minimum overlap. For #5: 40 x 5/8 = 25 inches. Always wire-tie splices securely and stagger them so they don't all occur at the same point.