{ "slug": "interior-paint-gallons-calculator", "title": "Interior Paint Gallons Calculator", "heading": "Interior Paint Gallons Calculator", "category": "other", "url": "https://www.revenuelab.fyi/toolbox/interior-paint-gallons-calculator", "summary": "Convert wall square footage into the exact number of gallons and coats you need to buy.", "description": "Interior wall paint typically covers 350-400 square feet per gallon on a single smooth coat, a figure printed on nearly every paint can label, but that number only tells half the story since almost every interior job needs two coats for even color and hide, especially over patched drywall, a color change, or a bold new hue going over white primer. This calculator takes your room's total wall length (perimeter) and ceiling height to compute gross wall area, subtracts an allowance for doors and windows so you're not buying paint for openings, then divides by your chosen coverage rate and multiplies by the number of coats. It rounds up to the nearest whole gallon since paint stores sell in gallon and 5-gallon increments and half-used cans of custom-tinted color are hard to match later. The default 350 sq ft/gallon coverage rate is a conservative real-world number that accounts for roller texture and slightly thicker application than the theoretical 400 sq ft ideal, so if you're a careful painter with a quality roller you may land under this estimate, but it's a safer number to shop with than the optimistic can label.", "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=interior-paint-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": "Number of coats", "kind": "number", "hint": null, "default": 2, "unit": null, "min": 1, "max": 3 }, { "id": "coveragePerGallon", "label": "Coverage per gallon", "kind": "number", "hint": null, "default": 350, "unit": "sq ft", "min": 200, "max": 450 } ], "outputs": [ { "id": "gallons", "label": "Gallons of paint", "format": "number", "hint": null, "primary": true }, { "id": "wallArea", "label": "Net wall area", "format": "number", "hint": "sq ft", "primary": false }, { "id": "totalPaintedArea", "label": "Total painted area (all coats)", "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", "Number of coats: 2", "Coverage per gallon: 350 sq ft" ], "outputs": [ "Gallons of paint: 3", "Net wall area: 408", "Total painted area (all coats): 816", "Exact gallons before rounding: 2.33" ] }, "how_to": { "title": "How to use this", "steps": [ "Enter room perimeter (ft).", "Enter wall height (ft).", "Enter doors & windows area (sq ft).", "Enter number of coats.", "Enter coverage per gallon (sq ft).", "Read your gallons of paint 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": 210 } }, { "name": "Typical", "description": "Defaults — the most common real-world setup.", "values": { "perimeter": 56, "height": 8, "openings": 40, "coats": 2, "coveragePerGallon": 350 } }, { "name": "Ambitious", "description": "Higher-end numbers — what if things really pop?", "values": { "perimeter": 90, "height": 8, "openings": 65, "coats": 3, "coveragePerGallon": 450 } } ], "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 wall area does a gallon of paint cover?", "a": "Most quality interior paints cover 350-400 sq ft per gallon on a smooth wall for one coat; 350 is a safer real-world planning number since texture, roller nap, and touch-ups eat into the theoretical maximum." }, { "q": "Do I really need two coats?", "a": "Almost always yes for a true color change, dark colors, or patched walls; a single coat over a similar existing color with a quality paint-and-primer product can sometimes suffice, but two coats is the standard for even, streak-free coverage." }, { "q": "Should I subtract doors and windows from wall area?", "a": "Yes, subtracting standard openings (a door is roughly 20 sq ft, a window roughly 15 sq ft) keeps you from overbuying, though many painters skip small deductions since trim work and cutting-in still use some paint." }, { "q": "Is it better to round up or buy exactly what's calculated?", "a": "Always round up to the next full gallon and consider buying slightly extra of a custom tint color, since color-matching a partial gallon later rarely produces an identical match." } ], "related": [ "https://www.revenuelab.fyi/toolbox/ceiling-paint-calculator", "https://www.revenuelab.fyi/toolbox/primer-gallons-calculator", "https://www.revenuelab.fyi/toolbox/exterior-paint-gallons-calculator" ], "license": "CC-BY-4.0", "citation": "RevenueLab — Interior Paint Gallons Calculator (https://www.revenuelab.fyi/toolbox/interior-paint-gallons-calculator)" }