Paint Calculator

What Is a Paint Coverage Calculator — Gallons per Room?

How many gallons of paint for any room with door/window deductions and multi-coat coverage. This calculator runs entirely in your browser — your data stays private, and no account is required.

How Much Paint Do You Need?

One gallon of paint covers approximately 350–400 square feet on smooth surfaces and 250–300 on textured surfaces. To calculate: measure the total wall area (height × width for each wall), subtract the area of doors (about 21 sq ft each) and windows (about 15 sq ft each), then divide by the coverage rate. Most rooms need two coats for proper coverage, especially when changing colors.

Calculating Wall Area

For a rectangular room: add up the width of all four walls, multiply by the ceiling height, then subtract openings. A 12×14-foot room with 8-foot ceilings has (12+14+12+14) × 8 = 416 sq ft of wall area. Subtract 2 doors (42 sq ft) and 2 windows (30 sq ft) = 344 sq ft of paintable surface. At 375 sq ft/gallon with 2 coats, you need about 2 gallons. For related home projects, see our Wallpaper Calculator.

Primary Color Mixing Results

Understanding Color Theory for Paint Mixing

Paint mixing follows subtractive color theory, where combining pigments absorbs more light and produces darker results. This is the opposite of additive color mixing used in screens, where combining light produces brighter results. The subtractive primary colors are red, yellow, and blue (or more precisely, magenta, yellow, and cyan in printing). Mixing any two primaries produces a secondary color: red and yellow make orange, blue and yellow make green, and red and blue make purple. Tertiary colors result from mixing a primary with an adjacent secondary, creating shades like red-orange, yellow-green, and blue-violet.

Complementary colors sit opposite each other on the color wheel. Mixing complementary colors in paint creates muted, brownish tones because the combination absorbs most of the visible spectrum. This property is useful for toning down overly bright colors without adding black, which can make colors look muddy. Adding a touch of green to an overly vivid red, for example, produces a richer, more natural red. Understanding these relationships helps you predict mixing results and correct off-target colors.

Paint Coverage by Surface Type

Coverage rates vary dramatically by surface condition. Smooth drywall with a primer coat absorbs the least paint, yielding 350 to 400 square feet per gallon. Textured surfaces like knockdown or orange peel reduce coverage to 250 to 300 square feet per gallon because paint fills the texture valleys. Bare wood absorbs paint heavily on the first coat, dropping coverage to 200 to 300 square feet per gallon; subsequent coats cover normally. Previously painted surfaces in good condition offer the best coverage because the old paint seals the substrate. Brick and masonry are the most paint-hungry surfaces, consuming up to twice the paint of smooth drywall due to their porous, irregular texture. For wallcovering alternatives, see our Wallpaper Calculator.

Choosing the Right Paint Finish

Paint finish (sheen level) affects both appearance and durability. Flat or matte finishes hide wall imperfections but stain easily and are difficult to clean, making them best for ceilings and low-traffic rooms. Eggshell offers a slight sheen with better washability, suitable for living rooms and bedrooms. Satin provides a soft luster and cleans well, making it the most popular choice for kitchens, bathrooms, and hallways. Semi-gloss resists moisture and scrubs clean easily, ideal for trim, cabinets, and doors. High-gloss creates a mirror-like finish that highlights imperfections but is extremely durable, typically reserved for accent pieces, furniture, and front doors.

Higher-sheen paints reflect more light, making colors appear slightly lighter and more saturated compared to flat paint of the same color. This means a color chip viewed on a flat card may look different when applied in semi-gloss. Paint stores can adjust formulations to compensate, but testing a sample on the actual surface under your room's lighting conditions is always the most reliable approach. Calculate project costs for larger renovations with our Fence Calculator and Deck Calculator.

Color Matching and Custom Mixing Tips

When mixing custom colors, always mix more than you think you need. Recreating an exact custom shade is extremely difficult because even small measurement variations change the result. If you need two gallons, mix three to ensure consistency across all walls. Start with the lighter base color and gradually add the darker color, mixing thoroughly after each addition. Record exact quantities so you can replicate the formula if needed. Use a paint mixing drill attachment for large volumes because hand stirring rarely achieves complete uniformity. Test the mixed color on a white surface and let it dry completely before judging, as wet paint typically dries one to two shades darker. For color code conversions between hex, RGB, and other formats, use our Hex to RGB Converter.

Estimating Paint for Different Room Configurations

Standard room calculations assume four rectangular walls, but real rooms have alcoves, soffits, vaulted ceilings, and accent walls that complicate the math. For vaulted ceilings, calculate the triangular wall section separately: area equals one-half times base times the additional height above the standard wall height. Cathedral ceilings in a 14-foot-wide room with a peak 4 feet above the 8-foot walls add approximately 28 square feet per end wall. Bay windows add three small wall sections; measure each panel individually and add the ceiling of the bay. Rooms with chair rails or wainscoting that use different colors above and below should be calculated as separate zones with independent coverage estimates.

Stairwells present the most complex painting scenarios because wall heights vary continuously. Measure the tallest wall height, calculate total area as if all walls were that height, then subtract approximately 25 to 30 percent for the stair-step reduction. Budget an extra half-gallon for waste and touch-ups in stairwells because the awkward angles and extension pole work increase spills and inconsistency. For broader home improvement project calculations, see our Concrete Calculator and Mulch Calculator.

Paint Quantity Planning and Waste Reduction

Buying the right amount of paint saves money and reduces waste. Round up to the next full gallon for single rooms because partial gallons cost more per ounce and you will need touch-up paint later. For multi-room projects using the same color, buy in five-gallon buckets to save 10 to 20 percent and ensure color consistency across cans. Most paint stores offer sample sizes (quarts or pints) for testing before committing to full gallons. Keep leftover paint sealed tightly with plastic wrap under the lid, store in a temperature-stable location between 50 and 80 degrees Fahrenheit, and label cans with the room, date, and color formula for future touch-ups. Latex paint stored properly lasts 2 to 10 years, while oil-based paint lasts up to 15 years. For calculating other material quantities in home projects, use our Gravel Calculator and Tile Calculator.

When planning a full home repaint, create a color flow chart that maps each room's wall color, trim color, and ceiling color. This prevents purchasing duplicate cans of the same shade under different names and ensures transitions between rooms feel intentional. Most designers recommend no more than three to five colors for an entire home interior, using variations in sheen rather than color to distinguish surfaces.