# Rebar vs Wire Mesh for a Concrete Slab Mesh and rebar compared for slabs on ground: what each does, how each is named, where it goes, and a worked steel count. Guide page: (published 2026-10-06, updated 2026-10-06). This Markdown version has the guide's key points, outline, FAQs and sources; the full article, with its worked examples and diagrams, is on the page. ## Key takeaways - In a slab on ground, reinforcement controls cracking and crack width: the Wire Reinforcement Institute (WRI) says concrete "by its very nature tends to crack", and the steel keeps the cracked pieces closely knit. - Welded wire is named by spacing and wire area: 6x6-W1.4xW1.4 has plain wires 6 in apart each way, each 0.014 sq in. Rebar is named by bar number, about its diameter in eighths of an inch, so #4 is about 1/2 in. - Under IRC Section R506.2.4, as adopted in Seattle, reinforcement that is provided must be supported between the center and the upper third of the slab during the pour; WRI advises against laying mesh on the ground and pulling it up. - Neither is better by default: WRI describes an engineer working out the steel area a slab needs and then supplying it as bars or as a welded wire style, so follow your plans and local code. - Steel fills well under 1% of the slab's volume in the worked example, so it doesn't change how much concrete to order. ## In this guide 1. [What reinforcement does in a slab](https://www.howmanyyardsdoineed.com/guides/rebar-vs-wire-mesh-for-concrete/#what-reinforcement-does) 2. [Welded wire mesh vs rebar](https://www.howmanyyardsdoineed.com/guides/rebar-vs-wire-mesh-for-concrete/#mesh-vs-rebar) 3. [Reading the sizes: 6x6-W1.4xW1.4 and #4](https://www.howmanyyardsdoineed.com/guides/rebar-vs-wire-mesh-for-concrete/#sizes-and-designations) 4. [Where reinforcement sits in the slab](https://www.howmanyyardsdoineed.com/guides/rebar-vs-wire-mesh-for-concrete/#where-it-goes) 5. [Supports, ties, and laps](https://www.howmanyyardsdoineed.com/guides/rebar-vs-wire-mesh-for-concrete/#supports-ties-and-laps) 6. [When plans or code call for it](https://www.howmanyyardsdoineed.com/guides/rebar-vs-wire-mesh-for-concrete/#when-it-is-required) 7. [Worked example: steel for a 12 × 20 ft slab](https://www.howmanyyardsdoineed.com/guides/rebar-vs-wire-mesh-for-concrete/#worked-example) 8. [What to order](https://www.howmanyyardsdoineed.com/guides/rebar-vs-wire-mesh-for-concrete/#what-to-order) ## Frequently asked questions ### Is wire mesh or rebar better for a concrete slab? Neither is better in general. WRI says the design process for welded wire is relatively the same as for rebar: an engineer calculates the area of steel the slab needs, then converts it to bars or to a welded wire style. Use the reinforcement your plans specify. ### Does wire mesh stop a concrete slab from cracking? No. WRI says concrete by its very nature tends to crack, and that welded wire's main job in a slab is to control cracking and crack widths, keeping the cracked sections closely knit so the slab acts as a unit. It notes that load transfer across a crack is usually ineffective once the crack is wider than 1/16 in. ### Where should wire mesh sit in a 4 inch slab? IRC Section R506.2.4, as adopted in Seattle, says reinforcement that is provided must be supported between the center and the upper third of the slab during the pour. In a 4 in slab that is 1.33 to 2 in below the top. WRI advises against laying mesh on the ground and pulling it up during the pour. ### What does 6x6 W1.4xW1.4 mean? It is a welded wire style: wires 6 in apart in both directions, both wire sizes W1.4. W means a plain wire, and the number is its area in hundredths of a square inch, so W1.4 is 0.014 sq in. WRI lists this style as the old 10 gauge, weighing about 0.21 lb per sq ft. ### What size is #4 rebar? About 1/2 in. CRSI defines the bar number as approximately the bar diameter in eighths of an inch. Caltrans's table of standard ASTM bar data lists #4 at 0.500 in nominal diameter, 0.20 sq in of area, and 0.668 lb per foot. ### Does the building code require mesh or rebar in a slab? IRC Section R506.2.4, as adopted in Seattle, says how reinforcement must be supported "where provided", not when it is needed. Local rules can go further: American Canyon, California, requires at least 6 by 6 inch, 10-gauge welded wire mesh or an approved alternate in slabs inside buildings. Ask your building department and follow your plans. ## Related calculators and guides ### Calculators - [Concrete Calculator](https://www.howmanyyardsdoineed.com/concrete-calculator/) — Slab volume in cubic feet, cubic yards, and cubic meters, with ready-mix order size and bag counts for documented products. ### Guides - [How to Pour a Concrete Slab](https://www.howmanyyardsdoineed.com/guides/how-to-pour-a-concrete-slab/) — Plan, form, mix, place, finish, joint, and cure a slab, following the manufacturer's published method. - [Pouring and Curing Concrete in Cold or Hot Weather](https://www.howmanyyardsdoineed.com/guides/concrete-in-cold-and-hot-weather/) — Temperature limits, freeze protection, hot-weather drying, and curing time for a new slab, with a worked example. - [Concrete Bag Yields by Bag Size](https://www.howmanyyardsdoineed.com/guides/concrete-bag-yields/) — Published cubic-foot yields for bagged concrete mixes, with bags per cubic foot, cubic yard, and cubic meter. ## Sources - [How to Specify, Order & Use Welded Wire Reinforcement in Light Construction (Tech Fact TF 202-R-21)](https://wirereinforcementinstitute.org/application/files/6416/8417/2727/TF_202-R-21_Specify_Order_Use.pdf) — Wire Reinforcement Institute. Used for: 6x6 W1.4xW1.4 (10 gauge) 0.21 lb/sq ft and 6x6 W2.9xW2.9 (6 gauge) 0.42 lb/sq ft; stock sheets 5–10 ft wide and 10–20 ft long; rolls 5–7 ft wide and 150–200 ft long; supports commonly 2–3 ft apart; aggregate interlock usually ineffective above 1/16 in crack width; drying shrinkage 1/2–1 in per 100 ft. Checked 2026-10-06. - [Supports Are Needed for Long-Term Performance of Welded Wire Reinforcement in Slabs-on-Grade (Tech Fact TF 702-R-21)](https://wirereinforcementinstitute.org/application/files/6216/2852/2594/TF_702-R-21_Slab_on_Grade.pdf) — Wire Reinforcement Institute. Used for: One layer at or above mid-depth, in general one-third of the depth below the surface; suggested support spacing 2–3 ft or less for wires smaller than W4/D4 spaced under 12 in. Checked 2026-10-06. - [Manual of Standard Practice: Structural Welded Wire Reinforcement (WWR-500-R-26)](https://wirereinforcementinstitute.org/application/files/7217/8472/2671/WWR-500-R-26_MSP.pdf) — Wire Reinforcement Institute. Used for: W = plain wire, D = deformed wire; the number is the wire's area in hundredths of a square inch (W4.6 = 0.046 sq in); a style gives the wire spacings, then the wire sizes. Checked 2026-10-06. - [Typical WPWR Lap Splice Detail, Slab-on-Ground (WWR.2)](https://wirereinforcementinstitute.org/application/files/6616/4296/2459/WWR.2_WPWR_LAP_SOG.pdf) — Wire Reinforcement Institute. Used for: 2 in minimum lap splice, measured between wire centerlines (drawn between the outermost wires of the two mats). Checked 2026-10-06. - [Welded Wire Reinforcement: Frequently Asked Questions](https://wirereinforcementinstitute.org/welded-wire-reinforcement/welded-wire-faqs) — Wire Reinforcement Institute. Used for: Wires up to 5/8 in diameter (equivalent to a #5 rebar); ACI 301 support spacing of 12 in for wires smaller than D4.0/W4.0. Checked 2026-10-06. - [Reinforced Concrete Terminology](https://www.crsi.org/reinforcing-basics/reinforced-concrete-terminology/) — Concrete Reinforcing Steel Institute (CRSI). Used for: Bar number ≈ bar diameter in eighths of an inch (#5 ≈ 5/8 in). Checked 2026-10-06. - [Reinforcing Bar Placing](https://www.crsi.org/reinforcing-basics/reinforced-concrete/placing-bars/) — Concrete Reinforcing Steel Institute (CRSI). Checked 2026-10-06. - [Bar Identification](https://www.crsi.org/reinforcing-basics/reinforcing-steel/bar-identification/) — Concrete Reinforcing Steel Institute (CRSI). Checked 2026-10-06. - [Bridge Design Details 13.1, Reinforcement: Table 13.1.1, ASTM Standard Reinforcing Bar Data (September 2025)](https://dot.ca.gov/-/media/dot-media/programs/engineering/documents/bridgedesigndetails/chapter-12/202509bddchapter13reinforcement-a11y.pdf) — California Department of Transportation (Caltrans). Used for: #3: 0.375 in, 0.11 sq in, 0.376 lb/ft; #4: 0.500 in, 0.20 sq in, 0.668 lb/ft; #5: 0.625 in, 0.31 sq in, 1.043 lb/ft; #6: 0.750 in, 0.44 sq in, 1.502 lb/ft. Checked 2026-10-06. - [2015 Seattle Residential Code, Chapter 5 Floors: Section R506, Concrete Floors (On Ground)](https://www.seattle.gov/documents/Departments/SDCI/Codes/SeattleResidentialCode/2015SRCChapter5.pdf) — City of Seattle, Department of Construction and Inspections. Used for: Slab-on-ground floors at least 3 1/2 in thick; reinforcement, where provided, supported from the center to the upper one-third of the slab during placement. Checked 2026-10-06. - [American Canyon Municipal Code 16.03.070: Amend Section R506.2.4 Reinforcement support](https://law.cityofamericancanyon.org/us/ca/cities/american-canyon/code/16.03.070) — City of American Canyon, California. Used for: Slabs inside a building reinforced with at least 6 × 6 in, 10-gauge welded wire mesh or an approved alternate. Checked 2026-10-06. **Estimate only.** Results are planning estimates computed from the numbers you enter. They are not engineering, structural, or code advice. Confirm quantities, product yields, and installation requirements with your supplier, the product label, and your local building authority before you order or build.