Interior Paint Calculator
Planning to paint a room? Enter the dimensions, number of doors and windows, and this calculator tells you how many gallons of paint to buy.
How to Calculate Paint for a Room
Start by measuring the room perimeter. Add the length and width, then multiply by 2. A 12 × 10 room has a perimeter of 44 feet. Multiply that by the ceiling height to get total wall area. At 8-foot ceilings, that is 352 square feet.
Subtract openings. A standard door is about 21 square feet, a window around 15 square feet. If the room has one door and two windows, subtract 51 square feet, leaving 301 square feet to paint.
Divide by 350, the coverage of one gallon of paint. Round up to the nearest gallon. For 301 square feet, you need one gallon for one coat, two gallons for two coats. Always buy enough for two coats for best results.
One Coat vs. Two Coats
Two coats deliver better coverage, deeper color, and longer-lasting results. The first coat seals the surface and evens out absorption. The second coat provides the final color and sheen.
One-coat paint exists, but it works best over similar colors or properly primed walls. Switching from dark to light, covering stains, or painting bare drywall all require at least two coats for uniform appearance.
Primer counts as the first coat when painting new drywall or switching from oil to latex. Use a quality primer, let it dry fully, then apply two finish coats for professional-grade results.
Choosing the Right Paint Finish
Flat or matte finishes hide wall imperfections but do not clean well. Use them on ceilings and low-traffic areas like formal dining rooms or adult bedrooms.
Eggshell and satin have a slight sheen and wash better than flat. They work for living rooms, hallways, and bedrooms. Satin is more durable and suits homes with kids or pets.
Semi-gloss and gloss are the toughest finishes. Use semi-gloss in kitchens, bathrooms, and on trim. High-gloss is rare on walls but common on doors, cabinets, and furniture for maximum durability and easy cleaning.
Frequently Asked Questions
How much area does a gallon of paint cover?
One gallon covers about 350 to 400 square feet with one coat. Textured walls, dark colors, or porous surfaces may reduce coverage to 300 square feet per gallon.
Do I need to paint the ceiling too?
Switch to the Walls & Ceiling mode if you plan to paint the ceiling. Ceiling paint is often flat or matte to hide imperfections and reduce glare.
Should I buy extra paint?
Yes. Buy at least one extra quart for touch-ups. Paint sheen and color can vary slightly between batches, so having leftovers from the original purchase ensures a perfect match.
How many coats of paint do I need?
Two coats are standard. Primer plus one finish coat works for light color changes. Dark-to-light or bold color changes may need two or three finish coats.
Do I subtract for trim and baseboards?
This calculator already subtracts standard door and window areas. You can ignore trim since it occupies minimal wall space and any extra paint covers touch-ups.