Rebar Calculator โ Estimate Rebar for Concrete Projects
Calculate rebar quantity for concrete slabs; footings; and walls. Get total linear feet and number of bars needed.
Rebar (reinforcing bar) strengthens concrete and prevents cracking. Proper spacing and coverage are critical for structural integrity. This calculator estimates rebar based on your slab size and grid spacing.
How much rebar for a concrete slab?
For a 10x10 slab with 12-inch spacing: you need 9 bars each way (18 total); each 10 feet long = 180 linear feet. With 20-foot standard bars; buy 9 bars plus overlap.
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How This Material Calculator Works
This calculator uses industry-standard formulas to estimate the quantity of materials needed for your project. It factors in standard waste allowances (typically 5-10% depending on material type) so you purchase enough without significant overbuying. Measurements are based on common product dimensions available at major retailers and building supply stores. For best results, measure your project area carefully and round up to the nearest whole unit when purchasing.
Tips for Accurate Material Estimates
Always measure twice before ordering materials. Account for cuts, corners, and irregular shapes by adding 10% extra for most materials. For concrete and masonry, consider the subgrade preparation and drainage requirements. Check local building codes before starting any project โ permits may be required for structural work, fencing over certain heights, or decks above ground level. Buy materials from the same batch to ensure color consistency, especially for tiles, pavers, and paint.
Key Information
| Parameter | Details |
|---|---|
| Common Size | #4 (1/2 inch) for slabs |
| Standard Grid Spacing | 12 or 18 inches on center |
| Rebar Length | 20 feet per standard bar |
| Cover from Edge | 3 inches minimum |
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Use Calculator NowFrequently Asked Questions
How much rebar for a concrete slab?
For a 10x10 slab with 12-inch spacing: you need 9 bars each way (18 total); each 10 feet long = 180 linear feet. With 20-foot standard bars; buy 9 bars plus overlap.
What size rebar for a patio slab?
Use #3 (3/8 inch) for 4-inch patios and walkways. Use #4 (1/2 inch) for driveways and 6-inch slabs. Use #5 (5/8 inch) for structural footings and foundations.
Does every concrete slab need rebar?
Not all โ small non-structural slabs (under 4 inches) can use wire mesh instead. But rebar is recommended for driveways; garage floors; patios over 100 sq ft; and any load-bearing concrete.
How much extra material should I order?
For most construction materials, order 10% extra to account for cuts, waste, breakage, and mistakes. For tiles and pavers, add 15% if using a diagonal or herringbone pattern. Concrete should include a 5-10% overage since running short mid-pour is costly. Always keep leftover materials for future repairs.
Do I need a permit for my project?
Permit requirements vary by location and project scope. Generally, structural work (walls, roofing, foundations), electrical, plumbing, fences over 6 feet, and decks above 30 inches require permits. Cosmetic work like painting, flooring, and landscaping usually does not. Check with your local building department before starting.
How do I convert between material units?
Common conversions: 1 cubic yard = 27 cubic feet. 1 square (roofing) = 100 sq ft. 1 board foot = 1 inch ร 12 inches ร 12 inches of lumber. Concrete is sold in cubic yards; multiply length ร width ร depth in feet and divide by 27. Our calculator handles these conversions automatically.
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Last updated: March 2026