{
  "slug": "primer-gallons-calculator",
  "title": "Primer Gallons Calculator",
  "heading": "Primer Gallons Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/primer-gallons-calculator",
  "summary": "Work out how much primer to buy before you ever open the topcoat can.",
  "description": "Primer typically covers slightly less area per gallon than finish paint — usually 300-350 sq ft per gallon versus 350-400 for topcoat — because primer is formulated to soak into and seal porous or patched surfaces like new drywall, bare wood, or repaired plaster rather than to lay flat and glossy. This calculator works exactly like an interior paint calculator: take your wall area (from perimeter times height, minus door and window openings), decide whether you need one coat of primer (standard for most repaints) or two (recommended for major color changes, stains, or bare drywall that will otherwise drink up your finish coat unevenly), then divide by the coverage rate and round up. Skipping or skimping on primer is one of the most common reasons a paint job needs a surprise third coat of finish paint, since unprimed patches and bare drywall absorb paint at a different rate than the surrounding wall, leaving visible flashing once it dries. Tinted primer (gray for dark topcoats, white for light ones) can also reduce the number of topcoat coats needed, which is worth factoring into your total project cost.",
  "formula": "Wall Area = (Perimeter × Height) − Openings. Gallons = ceil((Wall Area × Coats) ÷ Coverage per Gallon).",
  "dateModified": "2026-09-06",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=primer-gallons-calculator",
  "inputs": [
    {
      "id": "perimeter",
      "label": "Room perimeter",
      "kind": "number",
      "hint": null,
      "default": 56,
      "unit": "ft",
      "min": 4,
      "max": null
    },
    {
      "id": "height",
      "label": "Wall height",
      "kind": "number",
      "hint": null,
      "default": 8,
      "unit": "ft",
      "min": 6,
      "max": 20
    },
    {
      "id": "openings",
      "label": "Doors & windows area",
      "kind": "number",
      "hint": null,
      "default": 40,
      "unit": "sq ft",
      "min": 0,
      "max": null
    },
    {
      "id": "coats",
      "label": "Coats of primer",
      "kind": "number",
      "hint": null,
      "default": 1,
      "unit": null,
      "min": 1,
      "max": 2
    },
    {
      "id": "coveragePerGallon",
      "label": "Coverage per gallon",
      "kind": "number",
      "hint": null,
      "default": 300,
      "unit": "sq ft",
      "min": 150,
      "max": 400
    }
  ],
  "outputs": [
    {
      "id": "gallons",
      "label": "Gallons of primer",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "wallArea",
      "label": "Net wall area",
      "format": "number",
      "hint": "sq ft",
      "primary": false
    },
    {
      "id": "rawGallons",
      "label": "Exact gallons before rounding",
      "format": "decimal",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Room perimeter: 56 ft",
      "Wall height: 8 ft",
      "Doors & windows area: 40 sq ft",
      "Coats of primer: 1",
      "Coverage per gallon: 300 sq ft"
    ],
    "outputs": [
      "Gallons of primer: 2",
      "Net wall area: 408",
      "Exact gallons before rounding: 1.36"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter room perimeter (ft).",
      "Enter wall height (ft).",
      "Enter doors & windows area (sq ft).",
      "Enter coats of primer.",
      "Enter coverage per gallon (sq ft).",
      "Read your gallons of primer 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": {
        "perimeter": 34,
        "height": 8,
        "openings": 25,
        "coats": 1,
        "coveragePerGallon": 180
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "perimeter": 56,
        "height": 8,
        "openings": 40,
        "coats": 1,
        "coveragePerGallon": 300
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "perimeter": 90,
        "height": 8,
        "openings": 65,
        "coats": 2,
        "coveragePerGallon": 400
      }
    }
  ],
  "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": "Do I always need to prime before painting?",
      "a": "Not always — repainting a similar color over sound existing paint often doesn't need primer, but new drywall, bare wood, stains, major color changes, and patched areas all benefit significantly from a primer coat first."
    },
    {
      "q": "Why does primer cover less area per gallon than paint?",
      "a": "Primer is formulated to be absorbed into porous surfaces like raw drywall or wood, which means more of it soaks in rather than sitting on the surface, reducing effective coverage compared to a sealed-surface topcoat."
    },
    {
      "q": "Can tinted primer reduce the number of topcoat coats I need?",
      "a": "Yes, having your primer tinted toward your final color (gray-tinted for dark colors, for example) can let you get full coverage in one topcoat instead of two, which can offset the extra cost and time of priming."
    },
    {
      "q": "Is primer necessary over glossy paint?",
      "a": "Yes, primer or at minimum a deglossing step is important over high-gloss or semi-gloss existing paint since new paint won't adhere well to a slick glossy surface without it."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/interior-paint-gallons-calculator",
    "https://www.revenuelab.fyi/toolbox/ceiling-paint-calculator",
    "https://www.revenuelab.fyi/toolbox/drywall-sheets-calculator"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Primer Gallons Calculator (https://www.revenuelab.fyi/toolbox/primer-gallons-calculator)"
}