Paint Calculator

Enter a room's length, width and height, its doors and windows and the area one gallon covers, and get the paint for the walls, and the ceiling and primer if you add them, rounded up once to whole quarts with the gallon cans they make.

Estimates for planning, not professional advice. Read the full notice.

Room and coverage

Feet and inches, like 12' 6"

Feet and inches, like 12' 6"

Feet and inches, like 12' 6"

Like 120 sq ft

Like 120 sq ft

Like 120 sq ft

Like 120 sq ft

Like 120 sq ft

Example: a twelve by fourteen foot room

2.09 gal

  • Wall area to paint 365 ft²
  • Paint bought, whole quarts 2.25 gal
  • Cans: one gallon can 2 × 1 gal cans
  • Cans: one quart can 1 × 1 qt can

Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.

Shopping list

Example: a twelve by fourteen foot room
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    Worked example: a twelve by fourteen foot room

    Show the working
    1. Wall area before openings: the distance around the room times the wall height 52 ft × 8 ft = 416 ft²
    2. Take off the door and the two windows 416 ft² − 21 ft² − 15 ft² − 15 ft² = 365 ft²
    3. Paint: area times coats, divided by the area one gallon covers 365 ft² × 2 coats ÷ 350 ft² = 2.09 gal
    4. Round up once, to whole quarts, then pack them into pails, gallons and quarts 2.09 gal = 2.25 gal

    Assumptions

    The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.

    Coats of paint 2 coats[1]
    Default Benjamin Moore recommends two coats for its interior paint.
    Wall paint coverage 350 ft²/gal[2]
    Default PaintCare's figure to use when the coverage rate is unknown. The maker ranges are facts bm-n550-coverage and sw-k36-coverage.
    Benjamin Moore satin/pearl wall paint, spread rate, low end 400 ft²/gal[3]
    Benjamin Moore lists a spread rate of 400 to 450 sq ft per gallon for Regal Select Satin/Pearl N550, a wall paint.
    Benjamin Moore satin/pearl wall paint, spread rate, high end 450 ft²/gal[3]
    Benjamin Moore lists a spread rate of 400 to 450 sq ft per gallon for Regal Select Satin/Pearl N550, a wall paint.
    Sherwin-Williams interior matte paint, coverage, low end 350 ft²/gal[4]
    Sherwin-Williams lists a coverage of 350 to 400 sq ft per gallon at 4 mils wet for Emerald Interior Latex Matte K36.
    Sherwin-Williams interior matte paint, coverage, high end 400 ft²/gal[4]
    Sherwin-Williams lists a coverage of 350 to 400 sq ft per gallon at 4 mils wet for Emerald Interior Latex Matte K36.
    Ceiling paint coverage 400 ft²/gal
    Default Not read from a maker's own sheet. Check your label or supplier.
    Primer coverage 300 ft²/gal
    Default Not read from a maker's own sheet. Check your label or supplier.
    Surface roughness factor 1 times
    Default Our assumption; PaintCare says rough textures may need up to 50 percent more paint (fact paintcare-rough-more). Check your label or supplier.
    Door opening (width by height) 36 in × 84 in
    Default A common size, not sourced here. Check your label or supplier.
    Window opening (width by height) 36 in × 60 in
    Default A common size, not sourced here. Check your label or supplier.

    The example room at each published coverage rate

    Paint for the example room, two coats, at each coverage rate a source prints

    Source and end of rangeCoveragePaint, exactCans bought, as quarts
    PaintCare, most rates, low end 300 ft²/gal2.43 gal10 × 1 qt cans
    PaintCare, rate unknown (rough estimate) 350 ft²/gal2.09 gal9 × 1 qt cans
    PaintCare, most rates, high end 400 ft²/gal1.82 gal8 × 1 qt cans
    Sherwin-Williams interior matte, low end 350 ft²/gal (per Sherwin-Williams' data sheet, checked Nov 12, 2026)2.09 gal9 × 1 qt cans
    Sherwin-Williams interior matte, high end 400 ft²/gal (per Sherwin-Williams' data sheet, checked Nov 12, 2026)1.82 gal8 × 1 qt cans
    Benjamin Moore satin/pearl, low end 400 ft²/gal (per Benjamin Moore's data sheet, checked Nov 12, 2026)1.82 gal8 × 1 qt cans
    Benjamin Moore satin/pearl, high end 450 ft²/gal (per Benjamin Moore's data sheet, checked Nov 12, 2026)1.62 gal7 × 1 qt cans

    Product names are trademarks of their owners. HoneyDoMath is not affiliated with, sponsored by or endorsed by these makers. Figures come from each maker's published sheets and are shown for information only.

    Sources: [2][4][3]

    Each row is the same room and the same two coats; only the area one gallon covers changes. The cans are rounded up once, to quarts.

    Questions

    How much paint do I need for a room?

    Find the wall area, take off the doors and windows, multiply by the coats and divide by the area one gallon covers. The worked example does that for one room, and the calculator does it for your sizes and counts the cans once at the end.

    How much paint do I need for a bathroom?

    Enter the bathroom's length, width and wall height like any room. A small room often has a door and one window, so set those counts and the paint follows from the walls that are left.

    Do I subtract doors and windows?

    The Doors and windows choice does either. With it set to subtract, each door and window comes off at the sizes in the assumptions, which you can change. Set to count the walls whole, nothing comes off.

    How much primer do I need?

    Primer has its own coverage line, which you can change. It is one coat over the walls, and over the ceiling when the ceiling is painted too. The primer coverage is an input, not a sourced figure, so check the can.

    How many coats of paint?

    Benjamin Moore says two coats on bare surfaces and one or two on surfaces that were painted before, in the data sheet quoted under the sources. The calculator starts at two coats and lets you choose one, two or three.

    Sources (4)
    1. Regal® Select Premium Interior Paint & Primer Semi-Gloss N551, product data sheet, Benjamin Moore & Co., N551 US 062025 (data sheet, © 2022, 2025). Manufacturer data
      “While the high quality of our products sometimes makes one‐coat coverage achievable, Benjamin Moore® recommends two coats to achieve full color development and to optimize performance. On bare substrates, two coats are recommended; previously painted surfaces can be finished with 1 or 2 coats.”
      Per Benjamin Moore's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used
    2. Buy the Right Amount of Paint to Reduce Waste (Buy Right), PaintCare, web page, © 2026 PaintCare Inc.. Standards or industry body
      “Most coverage rates are between 300–400 square feed per gallon. If you don’t know the coverage rate, use 350 to get a rough estimate.”
      “Textured walls require more paint than smooth walls because they have more surface area. The greater the texture, the more paint is needed. You may need up to 50 percent more paint for rough textures.”
      Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used
    3. Regal® Select Premium Interior Paint & Primer Satin/Pearl N550, product data sheet, Benjamin Moore & Co., N550 US 040225 (data sheet, © 2022, 2025). Manufacturer data
      “Spread Rate Per Gallon 400 – 450 Sq. Ft.”
      Per Benjamin Moore's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used
    4. Emerald® Interior Latex Matte K36 Series, product data sheet, The Sherwin-Williams Company, K36 Series data sheet dated 08/2020. Manufacturer data
      “Coverage: 350 - 400 sq.ft. per gallon @ 4 mils wet; 1.6 mils dry”
      Per Sherwin-Williams' data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used

    These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.

    Sources

    • [1] Benjamin Moore, Regal® Select Premium Interior Paint & Primer Semi-Gloss N551, product data sheet. Checked November 12, 2026. https://media.benjaminmoore.com/WebServices/prod/assets/production/datasheets/TDS_0551/N551%20TDS%20US%20OKF.pdf
    • [2] PaintCare, Buy the Right Amount of Paint to Reduce Waste (Buy Right). Checked November 12, 2026. https://www.paintcare.org/buy-right/
    • [3] Benjamin Moore, Regal® Select Premium Interior Paint & Primer Satin/Pearl N550, product data sheet. Checked November 12, 2026. https://media.benjaminmoore.com/WebServices/prod/assets/production/datasheets/TDS_0550/N550_TDS_US.pdf
    • [4] Sherwin-Williams, Emerald® Interior Latex Matte K36 Series, product data sheet. Checked November 12, 2026. https://www.sherwin-williams.com/document/PDS/en/035777358153

    Made with HoneyDoMath.com. Estimates for planning; check product labels and local codes before you buy or build.