{
  "id": "quilt-backing",
  "version": "110a3836222c",
  "status": "published",
  "name": "Quilt Backing Calculator",
  "question": "How much quilt backing do I need?",
  "summary": "Works out how much backing fabric a quilt needs: the backing size with an overhang on each side, how many panels to sew together, and the yards to buy for regular or wide backing.",
  "category": "everyday-life",
  "subcategory": "clothing",
  "url": "https://www.acalculator.org/everyday-life/quilt-backing-calculator",
  "markdown": "https://www.acalculator.org/everyday-life/quilt-backing-calculator.md",
  "kind": "function",
  "method": "Backing = (width + 2 × extra) by (length + 2 × extra); panels = ⌈(span − 2 × seam) ÷ (fabric width − 2 × seam)⌉ each way; buy the smaller of panels × the other side, rounded up to 1/8 yd.",
  "assumptions": [
    "Panels are sewn side by side with one seam between neighbours; each seam uses the seam allowance on both panels.",
    "The fabric has no one-way print, so a panel can run either way.",
    "The length is rounded up to the next 1/8 yard (or 0.1 m), as fabric is usually cut."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "w": {
        "title": "Quilt top width",
        "description": "The finished width of the quilt top.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.0254,
        "maximum": 12.7
      },
      "l": {
        "title": "Quilt top length",
        "description": "The finished length of the quilt top.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.0254,
        "maximum": 12.7
      },
      "o": {
        "title": "Extra on each side",
        "description": "How far the backing reaches past the top on every side; 4 in is common, a longarm quilter may ask for more.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0,
        "maximum": 1.27
      },
      "fw": {
        "title": "Fabric width",
        "description": "The usable width of the backing fabric: about 42 in for quilting cotton, 108 in for wide backing.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.127,
        "maximum": 5.08
      },
      "sa": {
        "title": "Seam allowance",
        "description": "The seam allowance on each side of a seam that joins two panels; 1/2 in is common.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0,
        "maximum": 0.0508
      }
    }
  },
  "outputs": {
    "buy": {
      "label": "Backing to buy",
      "description": "The fabric length rounded up to the next 1/8 yard, and to the next 0.1 meter.",
      "format": "text"
    },
    "need": {
      "label": "Fabric length",
      "description": "Panels × the length of each panel, before rounding.",
      "format": "quantity",
      "unit": "in"
    },
    "layout": {
      "label": "Layout",
      "description": "How many panels to sew together and which way the seams run.",
      "format": "text"
    },
    "panels": {
      "label": "Panels",
      "description": "Widths of fabric sewn side by side.",
      "format": "integer"
    },
    "backWidth": {
      "label": "Backing width",
      "description": "Quilt width + 2 × the extra on each side.",
      "format": "quantity",
      "unit": "in"
    },
    "backLength": {
      "label": "Backing length",
      "description": "Quilt length + 2 × the extra on each side.",
      "format": "quantity",
      "unit": "in"
    },
    "yards": {
      "label": "Yards to buy",
      "description": "Rounded up to the next 1/8 yard.",
      "format": "number"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "w": 1.524,
      "l": 2.032,
      "o": 0.1016,
      "fw": 1.0668,
      "sa": 0.0127
    },
    "outputs": {
      "buy": "5 yd (4.5 m)",
      "need": 4.4704,
      "layout": "2 panels, seams running the length of the quilt",
      "panels": 2,
      "backWidth": 1.7272,
      "backLength": 2.2352,
      "yards": 5
    },
    "text": "A 60 in × 80 in quilt top needs a 68 in × 88 in backing: 2 panels, seams running the length of the quilt. Buy 5 yd (4.5 m)."
  },
  "examples": [
    {
      "given": {
        "w": 1.524,
        "l": 2.032,
        "o": 0.1016,
        "fw": 1.0668,
        "sa": 0.0127
      },
      "expect": {
        "panels": 2,
        "need": 4.4704,
        "yards": 5,
        "buy": "5 yd (4.5 m)",
        "backWidth": 1.7271999999999998
      },
      "source": "NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement (1 yard = 36 inches; 1 inch = 2.54 centimeters exactly), https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-03); hand calculation in content.mdx: backing 68 × 88 in; 2 panels × 88 in = 176 in = 4.89 yd, up to 5 yd"
    },
    {
      "given": {
        "w": 1.524,
        "l": 2.032,
        "o": 0.1016,
        "fw": 2.7432,
        "sa": 0.0127
      },
      "expect": {
        "panels": 1,
        "need": 1.7271999999999998,
        "yards": 2,
        "buy": "2 yd (1.8 m)",
        "layout": "One piece, no seams"
      },
      "source": "NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement (1 yard = 36 inches; 1 inch = 2.54 centimeters exactly), https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-03); hand calculation in content.mdx: one 108 in width turned sideways covers 88 in; cut 68 in = 1.89 yd, up to 2 yd"
    },
    {
      "given": {
        "w": 2.286,
        "l": 2.7432,
        "o": 0.1016,
        "fw": 1.0668,
        "sa": 0.0127
      },
      "expect": {
        "panels": 3,
        "need": 7.4676,
        "yards": 8.25,
        "layout": "3 panels, seams running across the quilt"
      },
      "source": "NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement (1 yard = 36 inches; 1 inch = 2.54 centimeters exactly), https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-03); hand calculation in content.mdx: backing 98 × 116 in; along: 3 × 116 = 348 in; across: 3 × 98 = 294 in = 8.17 yd, up to 8 1/4 yd"
    }
  ],
  "sources": [
    "NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement (1 yard = 36 inches; 1 inch = 2.54 centimeters exactly). https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-03)",
    "Deb’s Quilt Studio, Choosing the Right Quilt Backing Fabric (a longarm quilter asks for backing several inches larger than the top on each side, and prefers 108 in wide backing). https://debsquiltstudio.blog/choosing-the-right-quilt-backing-fabric/ (retrieved 2026-10-03)"
  ],
  "related": [
    "quilt-binding",
    "fabric",
    "yardage"
  ],
  "changelog": []
}