A rebar calculator tells you how many bars, how much linear footage, how much weight, and roughly how much material cost you need for a concrete slab. For a 20-by-20-foot slab on a 12-inch grid, plan on 42 bars totaling 840 linear feet of #4 rebar, or 22 bars and 440 feet at 24-inch spacing.
Enter your slab dimensions, grid spacing, and bar size below to get counts, footage, weight, and material cost for your project.
Rebar for concrete slabs & flatwork
Your complete rebar takeoff
| Component | Amount |
|---|---|
| Bars, long direction | - |
| Bars, short direction | - |
| Total linear feet | - |
| 20-ft sticks to order, including selected allowance | - |
| Estimated material cost | - |
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Rebar quantities for a 20 x 20 ft slab
The table below shows combined totals for both directions of a 20-by-20-foot slab using #4 rebar on a square grid.
| Grid spacing | Total bars | Linear feet | Approx. weight |
|---|---|---|---|
| 12 in | 42 | 840 ft | 561 lb |
| 16 in | 32 | 640 ft | 428 lb |
| 18 in | 28 | 560 ft | 374 lb |
| 24 in | 22 | 440 ft | 294 lb |
Bar weight varies by size: #3 bar weighs 0.376 pounds per foot, #4 weighs 0.668 pounds per foot, and #5 weighs 1.043 pounds per foot. At $0.50 to $1.00 per pound, material for a 20-by-20-foot slab typically runs about $150 to $560.
What affects rebar cost
- Grid spacing: Tighter spacing (12 inches) uses more bars; wider spacing (24 inches) uses fewer.
- Bar size: #4 is standard for slabs, while #5 adds strength and weight for heavier loads.
- Steel price: Material usually costs $0.50 to $1.00 per pound and moves with the market.
- Slab size: Bigger slabs need more bars in both directions, so footage scales with square footage.
What the estimate includes and does not include
The estimate covers rebar material only: bar counts, linear feet, weight, and material cost. It does not include the concrete itself, labor to tie and place the steel, chairs or supports, delivery, or taxes.
Frequently asked questions
Rebar or wire mesh — which should I use?
Rebar handles heavier loads and keeps slabs flatter, which is why it is preferred for driveways and structural slabs. Wire mesh is lighter and cheaper and works for low-stress patio slabs.
What spacing should I use for a driveway or patio?
Use #4 rebar at 12 to 18 inches on center for driveways. Patios can often use wider spacing or welded wire mesh depending on expected loads.
Does a 4-inch slab need rebar?
Rebar is recommended for driveways to resist vehicle weight and cracking. For light-use patios and walkways it is optional, though mesh or rebar still reduces crack risk.
Does the estimate include labor?
No. This calculator provides material only. Labor to cut, tie, and place rebar is priced separately by your concrete contractor.
Related tools
- Concrete Slab Cost Calculator
- Concrete Driveway Cost Calculator
- Concrete Column Calculator
- Post Hole Concrete Calculator
Sources and update policy
Bar weights follow standard industry sizing, and steel prices are reviewed monthly from public sources. See our methodology for how material costs are calculated.
Estimate transparency
How this estimate was prepared
- Prepared by
- GoHomeCost Cost Data Team
- Last reviewed
- August 24, 2026
- Update cycle
- Public price inputs checked monthly
Calculation method: Project quantity is multiplied by editable low, typical, and high unit rates. Selected location adjustments, waste, fixed charges, and minimum-job rules are then applied and shown in the result.
Public references used on this page:
This is a planning estimate, not a quote or structural specification. Check product yields, local code, site conditions, and written contractor bids before purchasing materials or building.
Read the full methodology Report a price or calculation issue