Paint Calculator

A paint calculator takes the guesswork out of estimating how much paint to buy for a room or whole-house project. By entering each room's dimensions and accounting for doors, windows, surface texture, and the number of coats, the calculator tells you exactly how many gallons to purchase — preventing both costly overbuying and frustrating mid-project shortages.

Paint coverage varies by product quality and surface condition. Standard interior latex paints cover approximately 350–400 square feet per gallon on a smooth, primed surface. Rough or heavily textured walls absorb more paint and can reduce coverage to 250–300 square feet per gallon. Premium self-priming paints sometimes advertise higher coverage, but real-world results on unprepared surfaces are usually closer to standard rates.

Interior painting is one of the highest-ROI home improvements available. A fresh coat of neutral paint can make a dated room feel modern and clean, and professional painters regularly cite interior painting as the number one cosmetic upgrade that speeds up a home sale. DIY interior painting costs primarily the materials — typically $25–$60 per gallon for quality paint — while professional labor adds $2–$6 per square foot of wall surface.

Follow these steps to get an accurate paint estimate for your project:

1. Add your rooms. Click "Add Room" for each space you plan to paint. Enter the room name, length, width, and ceiling height in feet. The calculator supports up to five rooms at once.
2. Enter door and window counts. Standard interior doors average 21 square feet and windows average 15 square feet. The calculator subtracts these from the total paintable wall area.
3. Choose surface texture. Smooth drywall yields ~350 sqft/gallon. Textured walls (orange peel, skip trowel) yield ~300 sqft/gallon. Heavily textured surfaces (knockdown, stucco) yield ~250 sqft/gallon.
4. Select number of coats. Same-color touch-ups typically need just 1 coat. New colors usually require 2. Going from a dark color to white or a light color often requires 3 coats for complete coverage.
5. Set your paint price. Entry-level paint costs $20–$30/gallon. Mid-range quality runs $35–$55. Premium and specialty paints can reach $70–$90/gallon but often provide better coverage and durability.
6. Specify if a primer is needed. When changing colors significantly, a separate primer coat seals the existing color and provides a neutral base. This reduces the number of finish coats needed and generally saves money overall.

• Always buy from the same dye lot. Paint mixed in separate batches can have subtle color variations. Buy all the cans you need at once to ensure a consistent color throughout the room.
• Order 10% extra. Even with accurate calculations, having an extra quart or small gallon on hand is invaluable for touch-ups after furniture moves or wall repairs months later. Store leftover paint in a tightly sealed can in a cool, dark location.
• Prep surfaces before painting. Filling nail holes, sanding rough patches, and cleaning walls of grease and dust makes paint adhere better and go further. A clean, sanded, and primed surface can improve coverage by 15–20%.
• Use the right applicator. Rollers with a 3/8-inch nap work well on smooth walls. Textured surfaces need a 1/2-inch or 3/4-inch nap to get paint into crevices. Cheap rollers shed fibers, so invest in quality.
• Cut-in before rolling. Apply paint along edges, corners, and trim with a brush before rolling the large wall areas. This prevents lap marks and produces a cleaner finish at boundaries.
• Consider sheen finish carefully. Flat/matte paint hides imperfections but is harder to clean — best for ceilings and adult bedrooms. Eggshell and satin finishes balance cleanability and a subtle glow, making them popular for living areas and hallways. Semi-gloss and gloss are ideal for trim, doors, and kitchens or bathrooms where moisture and scrubbing are common.