{
  "id": "concrete-block",
  "version": "179e50df3bb6",
  "status": "published",
  "name": "Concrete Block Calculator",
  "question": "How many blocks do I need for a wall?",
  "summary": "Counts the concrete blocks (CMU or cinder blocks) for a wall from its length, height and openings, with extra for cuts, plus the bags of mortar to lay them.",
  "category": "construction",
  "subcategory": "concrete",
  "url": "https://www.acalculator.org/construction/concrete-block-calculator",
  "markdown": "https://www.acalculator.org/construction/concrete-block-calculator.md",
  "kind": "function",
  "method": "Blocks = (length × height − openings) ÷ (nominal block length × nominal block height) × (1 + extra ÷ 100), rounded up; bags of mortar = blocks in the wall ÷ blocks per bag, rounded up.",
  "assumptions": [
    "Block sizes are nominal: the block plus one 3/8 in mortar joint. A standard 8 × 8 × 16 in block is 7 5/8 × 7 5/8 × 15 5/8 in and covers 16 × 8 = 128 in² of wall, so 1.125 blocks per ft².",
    "Extra for cuts and breakage: 10% by default (Nicolock orders 10% extra for its pavers); straight walls with few cuts need less.",
    "Mortar: 12 blocks per 80 lb bag by default (Sakrete Type S); type the number on your bag. Mortar is counted for the blocks in the wall, not the extra.",
    "Corners, bond beams, lintels, core fill and footings are not counted."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "l": {
        "title": "Wall length",
        "description": "The length of the wall.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "exclusiveMinimum": 0,
        "maximum": 1000
      },
      "h": {
        "title": "Wall height",
        "description": "The height of the wall.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "exclusiveMinimum": 0,
        "maximum": 1000
      },
      "o": {
        "title": "Openings",
        "description": "The total area of doors and windows in the wall, if any.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "area",
        "minimum": 0,
        "maximum": 1000000
      },
      "bl": {
        "title": "Block length (nominal)",
        "description": "The block’s length plus one mortar joint: 16 in for a standard block.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.01,
        "maximum": 2
      },
      "bh": {
        "title": "Block height (nominal)",
        "description": "The block’s height plus one mortar joint: 8 in for a standard block.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.01,
        "maximum": 2
      },
      "waste": {
        "title": "Extra for cuts and breakage",
        "description": "Blocks to add for cuts and breakage, in percent.",
        "type": "number",
        "x-unit": "percent",
        "minimum": 0,
        "maximum": 100
      },
      "bag": {
        "title": "Blocks per bag of mortar",
        "description": "How many blocks one bag of mortar lays, from the bag: 12 for an 80 lb bag of Sakrete Type S.",
        "type": "number",
        "minimum": 1,
        "maximum": 1000
      },
      "price": {
        "title": "Price per block",
        "description": "What one block costs. Leave empty to skip the cost.",
        "type": "number",
        "x-unit": "USD",
        "minimum": 0,
        "maximum": 10000
      }
    }
  },
  "outputs": {
    "blocks": {
      "label": "Blocks to buy",
      "description": "Net wall area ÷ one block’s nominal face × (1 + extra ÷ 100), rounded up.",
      "format": "integer"
    },
    "laid": {
      "label": "Blocks in the wall",
      "description": "Net wall area ÷ one block’s nominal face, before the extra.",
      "format": "number"
    },
    "bags": {
      "label": "Bags of mortar",
      "description": "Blocks in the wall ÷ blocks per bag, rounded up.",
      "format": "integer"
    },
    "squareFeet": {
      "label": "Wall area (ft²)",
      "description": "Length × height − openings, in square feet.",
      "format": "number"
    },
    "squareMeters": {
      "label": "Wall area (m²)",
      "description": "Length × height − openings, in square metres.",
      "format": "number"
    },
    "perSquareFoot": {
      "label": "Blocks per ft²",
      "description": "1 ÷ one block’s nominal face in square feet.",
      "format": "number"
    },
    "cost": {
      "label": "Cost of blocks",
      "description": "Blocks to buy × the price per block.",
      "format": "money"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "l": 6.096,
      "h": 1.2192,
      "o": 0,
      "bl": 0.4064,
      "bh": 0.2032,
      "waste": 10,
      "bag": 12
    },
    "outputs": {
      "blocks": 99,
      "laid": 90,
      "bags": 8,
      "squareFeet": 80,
      "squareMeters": 7.4322432,
      "perSquareFoot": 1.125
    },
    "text": "You need 99 blocks for 80 ft² of wall, and 8 bags of mortar."
  },
  "examples": [
    {
      "given": {
        "l": 6.096,
        "h": 1.2192,
        "o": 0,
        "bl": 0.4064,
        "bh": 0.2032,
        "waste": 10,
        "bag": 12
      },
      "expect": {
        "blocks": 99,
        "laid": 90,
        "bags": 8,
        "squareFeet": 80,
        "perSquareFoot": 1.125
      },
      "source": "hand calculation in content.mdx: 80 ft² × 1.125 = 90 blocks, × 1.1 = 99; 90 ÷ 12 = 7.5 → 8 bags; Archtoolbox, Concrete Block (CMU) Sizes, Shapes, and Finishes (nominal size = actual size + the 3/8 in mortar joint), https://www.archtoolbox.com/cmu-sizes-shapes-finishes/; Sakrete, Mortar Mix Type S (an 80 lb bag lays 12 standard 8 in blocks), https://www.sakrete.com/product/mortar-mix-type-s/; Nicolock, Simplify Your Project: How to Use a Paver Calculator (order 10 percent extra for waste), https://nicolock.com/2024/06/04/simplify-your-project-how-to-use-a-paver-calculator-for-accurate-estimates/"
    },
    {
      "given": {
        "l": 9.144,
        "h": 2.4384,
        "o": 1.9509638400000002,
        "bl": 0.4064,
        "bh": 0.2032,
        "waste": 5,
        "bag": 12,
        "price": 2.5
      },
      "expect": {
        "blocks": 259,
        "laid": 246.375,
        "bags": 21,
        "squareFeet": 219,
        "cost": 647.5
      },
      "source": "hand calculation in content.mdx: (240 − 21) × 1.125 = 246.375; × 1.05 = 258.69 → 259; Archtoolbox, Concrete Block (CMU) Sizes, Shapes, and Finishes (nominal size = actual size + the 3/8 in mortar joint), https://www.archtoolbox.com/cmu-sizes-shapes-finishes/; Sakrete, Mortar Mix Type S (an 80 lb bag lays 12 standard 8 in blocks), https://www.sakrete.com/product/mortar-mix-type-s/"
    },
    {
      "given": {
        "l": 5,
        "h": 2,
        "o": 0,
        "bl": 0.4,
        "bh": 0.2,
        "waste": 0,
        "bag": 12
      },
      "expect": {
        "blocks": 125,
        "laid": 125,
        "bags": 11,
        "squareMeters": 10
      },
      "source": "hand calculation in content.mdx: 10 m² ÷ 0.08 m² = 125; 125 ÷ 12 = 10.4 → 11; Archtoolbox, Concrete Block (CMU) Sizes, Shapes, and Finishes (nominal size = actual size + the 3/8 in mortar joint), https://www.archtoolbox.com/cmu-sizes-shapes-finishes/"
    }
  ],
  "sources": [
    "Archtoolbox, Concrete Block (CMU) Sizes, Shapes, and Finishes (the nominal dimension is the actual dimension plus the mortar joint; typical CMU mortar joints are 3/8 in). https://www.archtoolbox.com/cmu-sizes-shapes-finishes/ (retrieved 2026-10-02)",
    "Sakrete, Mortar Mix Type S (an 80 lb bag lays 12 standard 8 in block). https://www.sakrete.com/product/mortar-mix-type-s/ (retrieved 2026-10-02)",
    "Nicolock, Simplify Your Project: How to Use a Paver Calculator for Accurate Estimates (order 10 percent extra for waste). https://nicolock.com/2024/06/04/simplify-your-project-how-to-use-a-paver-calculator-for-accurate-estimates/ (retrieved 2026-10-01)",
    "NIST Special Publication 811, Appendix B (1 ft = 12 in = 0.3048 m exactly). https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02)"
  ],
  "related": [
    "concrete",
    "cubic-yards",
    "paver",
    "square-footage"
  ],
  "changelog": []
}