{
  "version": "v1",
  "source": "https://craftquantities.com",
  "licence": "CC BY 4.0",
  "licenceUrl": "https://creativecommons.org/licenses/by/4.0/",
  "attribution": "Craft Quantities — craftquantities.com",
  "documentation": "https://craftquantities.com/api/",
  "versioning": "Fields are added, never removed or repurposed, within a version. A breaking change becomes /api/v2/ and v1 keeps being built.",
  "slug": "concrete-calculator",
  "category": "materials-quantities",
  "title": "Concrete Calculator",
  "description": "Estimate how much concrete a slab needs — in cubic yards or cubic metres, and as a count of premix bags.",
  "url": "https://craftquantities.com/calculators/materials-quantities/concrete-calculator/",
  "json": "https://craftquantities.com/api/v1/calculators/concrete-calculator.json",
  "inputCount": 4,
  "testCaseCount": 2,
  "sourceCount": 2,
  "lastVerified": "2026-09-02",
  "citation": {
    "author": "Craft Quantities",
    "title": "Concrete Calculator",
    "version": "1.0.1",
    "sourcesChecked": "2026-09-02",
    "url": "https://craftquantities.com/calculators/materials-quantities/concrete-calculator/",
    "accessDate": null,
    "accessDateNote": "Add the date you retrieved this. It is deliberately absent: a static file cannot know when you read it, and the build date would be wrong.",
    "permanentVersionedUrl": null,
    "permanentVersionedUrlNote": "Not offered. This site keeps no archive of previous builds, so any such URL would resolve to the current page or to nothing. The version and sourcesChecked fields identify the calculation instead.",
    "formats": {
      "plain": "Craft Quantities. Concrete Calculator. Version 1.0.1. Sources checked 2026-09-02. https://craftquantities.com/calculators/materials-quantities/concrete-calculator/",
      "apa": "Craft Quantities. (2026). Concrete Calculator (Version 1.0.1) [Web calculator]. Retrieved from https://craftquantities.com/calculators/materials-quantities/concrete-calculator/",
      "harvard": "Craft Quantities (2026) Concrete Calculator (Version 1.0.1). Available at: https://craftquantities.com/calculators/materials-quantities/concrete-calculator/",
      "bibtex": "@misc{craftquantities-calculators-materials-quantities-concrete-calculator,\n  author       = {{Craft Quantities}},\n  title        = {Concrete Calculator},\n  version      = {1.0.1},\n  year         = {2026},\n  howpublished = {\\url{https://craftquantities.com/calculators/materials-quantities/concrete-calculator/}},\n}"
    }
  },
  "inputs": [
    {
      "id": "slabLength",
      "label": "Slab Length",
      "type": "number",
      "dimension": "length",
      "defaultValue": 3,
      "min": 0.01,
      "max": 50,
      "step": 0.1,
      "help": "The length of the slab or footing."
    },
    {
      "id": "slabWidth",
      "label": "Slab Width",
      "type": "number",
      "dimension": "length",
      "defaultValue": 3,
      "min": 0.01,
      "max": 50,
      "step": 0.1,
      "help": "The width of the slab or footing."
    },
    {
      "id": "slabThickness",
      "label": "Slab Thickness",
      "type": "number",
      "dimension": "length",
      "defaultValue": 0.1,
      "min": 0.01,
      "max": 1,
      "step": 0.01,
      "help": "How deep the concrete pour is."
    },
    {
      "id": "wasteFactorPercent",
      "label": "Waste Factor (%)",
      "type": "number",
      "defaultValue": 10,
      "min": 0,
      "max": 25,
      "step": 1,
      "help": "Extra concrete for spillage, uneven subgrade, and forming imprecision."
    }
  ],
  "sources": [
    {
      "label": "Standard formula: cubic yards = length (ft) x width (ft) x thickness (ft) / 27"
    },
    {
      "label": "An 80 lb bag of pre-mixed concrete yields approximately 0.6 cubic feet once mixed"
    }
  ],
  "testCases": [
    {
      "name": "3x3m slab, 0.1m thick, 10% waste",
      "inputs": {
        "slabLength": 3,
        "slabWidth": 3,
        "slabThickness": 0.1,
        "wasteFactorPercent": 10
      },
      "expected": 1.29,
      "toleranceDecimalPlaces": 1,
      "unit": "cubic yards",
      "confidence": "high",
      "steps": [
        {
          "label": "Volume (no waste)",
          "value": 0.9,
          "unit": "m³"
        },
        {
          "label": "Volume with waste factor",
          "value": 0.9900000000000001,
          "unit": "m³"
        },
        {
          "label": "Cubic feet",
          "value": 34.96152005427371,
          "unit": "ft³"
        },
        {
          "label": "80 lb bags needed",
          "value": 59,
          "unit": "bags"
        }
      ],
      "basis": "ambiguous"
    },
    {
      "name": "6x4m slab, 0.15m thick, 5% waste",
      "inputs": {
        "slabLength": 6,
        "slabWidth": 4,
        "slabThickness": 0.15,
        "wasteFactorPercent": 5
      },
      "expected": 4.94,
      "toleranceDecimalPlaces": 1,
      "unit": "cubic yards",
      "confidence": "high",
      "steps": [
        {
          "label": "Volume (no waste)",
          "value": 3.5999999999999996,
          "unit": "m³"
        },
        {
          "label": "Volume with waste factor",
          "value": 3.78,
          "unit": "m³"
        },
        {
          "label": "Cubic feet",
          "value": 133.48944020722686,
          "unit": "ft³"
        },
        {
          "label": "80 lb bags needed",
          "value": 223,
          "unit": "bags"
        }
      ],
      "basis": "ambiguous"
    }
  ],
  "usedByAssemblies": [
    {
      "id": "concrete-slab",
      "name": "Concrete slab"
    },
    {
      "id": "basement-conversion",
      "name": "Basement or cellar conversion"
    },
    {
      "id": "extension-shell",
      "name": "Extension shell, one or two storeys"
    },
    {
      "id": "porch-addition",
      "name": "Porch addition"
    },
    {
      "id": "garden-room",
      "name": "Garden room or backyard office"
    }
  ]
}