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  "name": "How do you calculate rebar for a concrete slab?",
  "description": "For a grid at 18-inch spacing, divide each slab dimension by 1.5 feet, round up, and multiply by the other dimension. A 20×20 ft slab needs 14 bars each way: 14 × 20 × 2 = 560 linear feet, plus 10% for laps and cuts — about 620 feet, or 31 twenty-foot #4 bars.",
  "url": "https://www.revenuelab.fyi/answers/how-to-calculate-rebar-for-a-slab",
  "dateModified": "2026-10-01",
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    "@type": "Organization",
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    "url": "https://www.revenuelab.fyi"
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  "license": "https://creativecommons.org/licenses/by/4.0/",
  "keywords": [
    "Concrete Slab Material Calculator",
    "Concrete Cost Calculator",
    "Concrete Slab Cost Calculator",
    "Concrete Slab Material Calculator"
  ],
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  "json": {
    "type": "answer",
    "question": "How do you calculate rebar for a concrete slab?",
    "shortAnswer": "For a grid at 18-inch spacing, divide each slab dimension by 1.5 feet, round up, and multiply by the other dimension. A 20×20 ft slab needs 14 bars each way: 14 × 20 × 2 = 560 linear feet, plus 10% for laps and cuts — about 620 feet, or 31 twenty-foot #4 bars.",
    "tableTitle": "Worked example: 20×20 ft slab, #4 rebar at 18 in on center",
    "columns": [
      "Step",
      "Math",
      "Result"
    ],
    "rows": [
      {
        "label": "Bars across 20 ft",
        "value": "20 ÷ 1.5 = 13.3",
        "note": "Round up to 14"
      },
      {
        "label": "Linear feet (both ways)",
        "value": "14 × 20 × 2",
        "note": "560 ft"
      },
      {
        "label": "Add 10% laps/waste",
        "value": "560 × 1.10",
        "note": "616 ft"
      },
      {
        "label": "20-ft bars to buy",
        "value": "616 ÷ 20",
        "note": "31 bars"
      }
    ],
    "context": "Placement matters more than quantity: rebar does its work in the lower-middle third of the slab — chairs or dobies holding it 2 inches up in a 4–6 inch slab — because rebar lying on the ground adds almost nothing. Wire mesh is the cheaper alternative for patios and walkways; rebar is worth it for driveways and garages. Lap splices need 24–40 bar diameters (12–16 inches for #4), which is where the 10% allowance goes.",
    "methodology": "Grid count = ⌈dimension ÷ spacing⌉ + edge bar per direction. Spacing (12–18 in on center for #4 in residential slabs) and lap lengths follow ACI 318 development-length basics simplified for flatwork.",
    "dateModified": "2026-10-01",
    "relatedCalculators": [
      {
        "label": "Concrete Slab Material Calculator",
        "to": "/concrete-slab-material-calculator"
      },
      {
        "label": "Concrete Cost Calculator",
        "to": "/concrete-cost-calculator"
      },
      {
        "label": "Concrete Slab Cost Calculator",
        "to": "/concrete-slab-cost-calculator"
      },
      {
        "label": "Concrete Slab Material Calculator",
        "to": "/concrete-slab-material-calculator"
      }
    ],
    "relatedReading": [
      {
        "label": "Concrete for a slab",
        "to": "/answers/how-to-calculate-concrete-for-a-slab"
      }
    ]
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}