{
  "slug": "concrete-slab-20x20-calculator",
  "title": "20x20 Concrete Slab Calculator",
  "heading": "20x20 Concrete Slab Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/concrete-slab-20x20-calculator",
  "summary": "Yardage for a full 400 sq ft slab — garage, large patio, or detached garage footing pad.",
  "description": "A 20x20 slab, at 400 square feet, is the classic footprint for a two-car detached garage and represents a large enough pour that ordering strategy really matters: this is squarely in ready-mix truck territory, not bagged concrete, and getting the yardage right avoids either an expensive second short-load delivery or paying for unused concrete. This calculator fixes the area at 400 square feet and lets you set thickness (garage slabs bearing vehicle weight are commonly poured at 4-5 inches over a compacted gravel base, sometimes thicker at the perimeter footing) and waste factor, then returns the cubic yards to order. At this size, a single standard ready-mix truck holds about 10 cubic yards, so the tool also shows how many truck loads your pour would need, which matters for scheduling a pour that has to finish before the leading edge sets up.",
  "formula": "Volume = 400 sq ft × Thickness(ft) ÷ 27, × (1 + Waste%). Truck loads = Cubic Yards ÷ 10 (typical truck capacity).",
  "dateModified": "2026-09-06",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=concrete-slab-20x20-calculator",
  "inputs": [
    {
      "id": "thicknessIn",
      "label": "Slab thickness",
      "kind": "number",
      "hint": null,
      "default": 4,
      "unit": "in",
      "min": 3,
      "max": 10
    },
    {
      "id": "wastePct",
      "label": "Waste factor",
      "kind": "number",
      "hint": null,
      "default": 10,
      "unit": "%",
      "min": 0,
      "max": 25
    },
    {
      "id": "truckCapacity",
      "label": "Truck capacity",
      "kind": "number",
      "hint": null,
      "default": 10,
      "unit": "cu yd",
      "min": 5,
      "max": 12
    }
  ],
  "outputs": [
    {
      "id": "cubicYards",
      "label": "Ready-mix needed",
      "format": "decimal",
      "hint": "cu yd",
      "primary": true
    },
    {
      "id": "truckLoads",
      "label": "Truck loads (at capacity)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "cubicFeet",
      "label": "Total cubic feet",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "area",
      "label": "Slab area",
      "format": "number",
      "hint": "sq ft",
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Slab thickness: 4 in",
      "Waste factor: 10 %",
      "Truck capacity: 10 cu yd"
    ],
    "outputs": [
      "Ready-mix needed: 5.43",
      "Truck loads (at capacity): 0.54",
      "Total cubic feet: 133.3",
      "Slab area: 400"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter slab thickness (in).",
      "Enter waste factor (%).",
      "Enter truck capacity (cu yd).",
      "Read your ready-mix needed on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "thicknessIn": 3,
        "wastePct": 6,
        "truckCapacity": 6
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "thicknessIn": 4,
        "wastePct": 10,
        "truckCapacity": 10
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "thicknessIn": 6.4,
        "wastePct": 16,
        "truckCapacity": 12
      }
    }
  ],
  "limitations": [
    "Estimates assume standard, average conditions — local rules, pricing, and materials vary.",
    "Results are rounded for readability; add a buffer before ordering, booking, or committing.",
    "Double-check anything with a real cost attached against a local quote."
  ],
  "faq": [
    {
      "q": "How many cubic yards of concrete for a 20x20 garage slab?",
      "a": "At 4 inches thick, about 4.94 cubic yards raw, roughly 5.4-5.5 cubic yards with a 10% waste factor — comfortably a little over half of one standard 10-yard truck."
    },
    {
      "q": "Should a garage slab be thicker than a patio?",
      "a": "Yes, garage slabs bearing vehicle weight are typically poured 4-5 inches minimum, sometimes with a thickened edge (turned-down footing) around the perimeter for wall support, versus the 3.5-4 inch standard for a walking patio."
    },
    {
      "q": "Can one truck deliver the whole 20x20 pour?",
      "a": "Usually yes at 4-5 inches thick, since that's under 6 cubic yards and most trucks carry 9-10 yards; thicker pours (6+ inches with reinforcement) can approach or exceed a single truck's capacity."
    },
    {
      "q": "What happens if I underestimate and the truck runs short?",
      "a": "A second truck has to be dispatched while the first pour is already setting, risking a visible cold joint; ordering slightly over your calculated need (or confirming with the batch plant) is cheaper insurance than a mid-pour shortage."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/concrete-slab-12x12-calculator",
    "https://www.revenuelab.fyi/toolbox/concrete-cubic-yards-calculator",
    "https://www.revenuelab.fyi/toolbox/rebar-length-calculator"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — 20x20 Concrete Slab Calculator (https://www.revenuelab.fyi/toolbox/concrete-slab-20x20-calculator)"
}