{
  "slug": "30x40-concrete-slab-calculator",
  "title": "30x40 Concrete Slab Calculator",
  "heading": "30x40 Concrete Slab Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/30x40-concrete-slab-calculator",
  "summary": "Yardage and cost for a 30x40 pole barn or shop slab, defaulted at 5 inches thick.",
  "description": "30x40 is a popular footprint for a pole barn, workshop, or large detached garage — 1,200 square feet of slab that adds up fast in material cost. This calculator defaults to 5 inches thick for equipment-bearing use and returns the ready-mix cubic yardage, an approximate bag count if hand-mixing any portion, and total cost at your local price per yard.",
  "formula": "Cubic Yards = (Length × Width × Thickness in inches ÷ 12) ÷ 27 × (1 + Waste%). Cost = Cubic Yards × Price per Yard.",
  "dateModified": "2026-09-06",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=30x40-concrete-slab-calculator",
  "inputs": [
    {
      "id": "length",
      "label": "Slab length",
      "kind": "number",
      "hint": null,
      "default": 40,
      "unit": "ft",
      "min": 1,
      "max": null
    },
    {
      "id": "width",
      "label": "Slab width",
      "kind": "number",
      "hint": null,
      "default": 30,
      "unit": "ft",
      "min": 1,
      "max": null
    },
    {
      "id": "thickness",
      "label": "Thickness",
      "kind": "number",
      "hint": null,
      "default": 5,
      "unit": "in",
      "min": 2,
      "max": 12
    },
    {
      "id": "waste",
      "label": "Waste factor",
      "kind": "number",
      "hint": null,
      "default": 10,
      "unit": "%",
      "min": 0,
      "max": 30
    },
    {
      "id": "pricePerYard",
      "label": "Ready-mix price per cubic yard",
      "kind": "number",
      "hint": null,
      "default": 150,
      "unit": "$",
      "min": 0,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "cubicYards",
      "label": "Ready-mix needed",
      "format": "decimal",
      "hint": null,
      "primary": true
    },
    {
      "id": "bags",
      "label": "80-lb bags (DIY mix)",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "cost",
      "label": "Estimated concrete cost",
      "format": "currency",
      "hint": null,
      "primary": false
    },
    {
      "id": "cubicFeet",
      "label": "Total cubic feet",
      "format": "decimal",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Slab length: 40 ft",
      "Slab width: 30 ft",
      "Thickness: 5 in",
      "Waste factor: 10 %",
      "Ready-mix price per cubic yard: 150 $"
    ],
    "outputs": [
      "Ready-mix needed: 20.37",
      "80-lb bags (DIY mix): 917",
      "Estimated concrete cost: $3,056",
      "Total cubic feet: 500"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter slab length (ft).",
      "Enter slab width (ft).",
      "Enter thickness (in).",
      "Enter waste factor (%).",
      "Enter ready-mix price per cubic yard ($).",
      "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": {
        "length": 24,
        "width": 18,
        "thickness": 3,
        "waste": 6,
        "pricePerYard": 90
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "length": 40,
        "width": 30,
        "thickness": 5,
        "waste": 10,
        "pricePerYard": 150
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "length": 64,
        "width": 48,
        "thickness": 8,
        "waste": 16,
        "pricePerYard": 240
      }
    }
  ],
  "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 much concrete does a 30x40 slab need?",
      "a": "At 5 inches thick with 10% waste, roughly 20.4 cubic yards — enough that most suppliers will schedule a dedicated truck run or two."
    },
    {
      "q": "Should a 30x40 pole barn slab be thicker than 5 inches?",
      "a": "If it will hold heavy equipment like tractors or lifts, 6 inches with rebar reinforcement is common; 4 inches is enough for light storage only."
    },
    {
      "q": "Is it cheaper to pour 30x40 in sections?",
      "a": "Pouring in one continuous placement with control joints cut afterward is usually cheaper and stronger than separate pours, since cold joints between separate pours are a common crack point."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/30x40-pole-barn-calculator",
    "https://www.revenuelab.fyi/toolbox/24x24-garage-calculator"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — 30x40 Concrete Slab Calculator (https://www.revenuelab.fyi/toolbox/30x40-concrete-slab-calculator)"
}