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Paint Coverage Calculator

Calculate exactly how much paint you need for walls, ceilings, and trim based on surface type and coating requirements.

Estimate paint quantity by room dimensions, surface condition, and color change severity. Accounts for primer needs on new drywall, additional coats for dark-to-light transitions, and spray application waste. Returns gallons needed with a practical overage allowance so you buy once.

Pro Tip: New drywall soaks up 10-15% more paint than previously painted surfaces. Always prime bare drywall with a dedicated primer rather than relying on paint-and-primer-in-one products, which still require two coats and cost more per gallon than a separate primer plus topcoat.

Hanging new drywall before painting? Estimate your sheet count and joint compound first.

Drywall Estimator →

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Paint Coverage Calculator
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How It Works

  1. Enter Room Dimensions

    Input the length, width, and ceiling height for each room. The calculator computes gross wall area and ceiling area automatically.

  2. Subtract Openings

    Enter the number of standard doors (21 sq ft each) and windows (15 sq ft each), or input custom opening sizes. These are deducted from the paintable area.

  3. Select Surface Type

    Choose the surface condition: previously painted, new drywall, bare wood, or textured. Each has a different coverage rate per gallon.

  4. Set Color Change

    Indicate whether you are repainting with a similar color (2 coats) or making a drastic color change like dark to light (3 coats). This directly affects total gallons.

  5. Choose Application Method

    Select brush/roller or spray. Spraying adds roughly 20-30% material waste compared to rolling, depending on surface geometry and overspray.

  6. Review Results

    The calculator returns total gallons for walls, ceiling, and trim separately, plus a 10% overage buffer for touch-ups and future repairs.

Built For

  • Homeowners repainting a bedroom or living room who want to buy the right number of gallons in a single trip.
  • Contractors preparing material takeoffs for interior repaint bids, broken down by primer and finish coats.
  • Property managers estimating paint quantities for tenant turnover across multiple identical units.
  • DIYers converting a dark accent wall to a lighter color and needing to account for extra coats.

Assumptions

  • Standard door openings are 21 sq ft (3' x 7') and standard windows are 15 sq ft (3' x 5').
  • Base coverage rate of 350 sq ft per gallon on smooth, previously painted surfaces.
  • Spray waste factor of 25% for typical residential interior work.

Limitations

  • Does not account for highly porous surfaces like unsealed masonry or heavily patched areas that may require additional primer.
  • Trim paint calculations assume standard baseboard and casing widths. Custom millwork may require separate measurement.

References

  • Paint coverage rates based on published manufacturer specifications from Benjamin Moore, Sherwin-Williams, and Behr product data sheets.
  • Spray waste factors from the Painting and Decorating Contractors of America (PDCA) estimating guidelines.

Frequently Asked Questions

Most interior latex paints cover 350-400 sq ft per gallon on smooth, previously painted surfaces. Porous surfaces like new drywall or bare wood drop coverage to 250-350 sq ft per gallon. Always check the manufacturer's spec on the can, since high-hide formulas and flat sheens tend to cover more than glossy finishes.
If the existing paint is in good condition and you are staying in the same color family, you can skip a separate primer. However, you should always prime when covering stains, going from dark to light, painting over glossy finishes, or coating new drywall. A dedicated primer costs about half as much per gallon as finish paint.
Two coats is standard for a same-color repaint. Going from a dark color to a significantly lighter one typically requires three coats, or two coats over a tinted primer. One coat is rarely sufficient except for minor touch-ups with an exact color match.
Add 10% to your calculated quantity for roller and brush work. For spray application, add 25-35% depending on how much masking you do. Keep at least a quart of each color for future touch-ups, stored with the lid sealed tightly and the room and color noted on the can.
Ceiling paint is formulated thicker to reduce drips, so coverage is typically 350-400 sq ft per gallon, similar to flat wall paint. The main difference is that ceilings are usually a single color with no cutting-in around trim, so waste is lower. Most rooms need only one gallon for the ceiling.
Rolling uses 20-30% less paint than spraying because there is no overspray. Spraying is faster on large open areas like new construction, but the time saved on application is partially offset by the extra masking required. For a single room repaint, rolling is almost always more practical.
Heavy texture like knockdown or orange peel increases surface area by 15-25% compared to smooth walls. Use the lower end of the manufacturer's coverage range (around 300 sq ft per gallon) and plan on two full coats. Back-rolling after spraying is the best way to get full coverage in texture valleys.
Disclaimer: Verify all calculations independently before purchasing. Actual coverage varies by manufacturer, surface condition, application method, and paint sheen.

Learn More

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How to Estimate Paint for Any Project

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