How to Calculate Paint Needs for Any Room

Buying too much paint is expensive, buying too little is frustrating. Here is how you get it right.

To calculate your paint needs, you can use our Paint Calculator or manually multiply the length of the room by the height for each wall and add the sums together to get the total wall area in square feet. Then you subtract the area for windows and doors (a standard door is about 20 sq ft and a window 15 sq ft). Normally, one gallon of high-quality paint covers about 350-400 square feet, depending on the surface and if it absorbs a lot of paint. Keep in mind that you almost always need to paint at least two coats, so multiply your paint needs by two!

Preparing the Surface

No matter how expensive the paint is, it will look terrible if the wall isn't prepared properly. Start by washing the walls to remove dust and grease. Fill any nail holes or cracks with spackle, let it dry, and sand it smooth. If you are painting over a very dark color with a light color, or painting over raw drywall, you absolutely must use a primer first. Primer seals the surface and provides a uniform base, reducing the number of topcoats you will need.

Choosing the Right Sheen

The finish of the paint (sheen) affects both durability and appearance. Flat or matte finishes hide imperfections well but are hard to clean. Eggshell and satin have a slight shine, are easier to wipe down, and are perfect for living rooms and bedrooms. Semi-gloss is highly durable and moisture-resistant, making it the standard choice for bathrooms, kitchens, and all baseboards or trim.

Expert Tip

Always box your paint! If you buy three gallons of the same color, mix them all together in a larger 5-gallon bucket before painting. This ensures a perfectly uniform color across the entire room, as slight variations can occur between individual cans during mixing at the store.

Summary

Accurate measurement is the key to a stress-free painting project. By calculating the total square footage, subtracting the doors and windows, and factoring in two coats, you will buy exactly what you need. A well-prepared wall and the right sheen will ensure a professional-looking finish that lasts for years.