Paint Calculator

How the Paint Calculator Works

This paint calculator estimates the amount of paint required to cover the walls of one or more rooms in your home. It works by computing the total wall surface area from the room's length, width, and height, then subtracting the area occupied by doors and windows. Each standard door is approximately 21 square feet and each standard window is about 15 square feet. The remaining paintable area is then divided by the paint coverage rate, which varies depending on the paint type. Interior wall paint typically covers 350 square feet per gallon, ceiling paint covers about 400, and exterior or trim paint covers around 300 square feet per gallon. Multiply by the number of coats you plan to apply and you have the total gallons needed.

The calculator supports multiple rooms so you can estimate paint for an entire house in one session. Each room has independent dimensions, door count, and window count. The results show a per-room breakdown alongside the total gallons and estimated cost, giving you a complete shopping list before heading to the paint store. All calculations happen in your browser with no data sent anywhere.

Tips for Estimating Paint Accurately

Getting an accurate paint estimate saves both money and trips to the store. Always round up to the nearest full gallon since most stores do not sell partial gallons of custom-mixed colors. If you are painting over a dark color with a lighter shade, plan for at least two to three coats and consider using a tinted primer as the first coat. Textured walls such as knockdown, orange peel, or popcorn ceilings absorb more paint and may reduce coverage by 10 to 20 percent. In those cases, lower the coverage rate in the calculator to account for the extra paint absorbed by the texture.

Measure each wall individually if your room is not a perfect rectangle. For rooms with vaulted ceilings, use the average wall height. Always buy slightly more than calculated since you will need extra for touch-ups after furniture is moved back in. Most paint stores allow returns of unopened gallons, so buying one extra is a low-risk strategy. Store leftover paint in a cool, dry place with a tight seal for future touch-ups, which can last for several years.

Understanding Paint Coverage Rates

Paint coverage rate describes how many square feet one gallon of paint can cover in a single coat on a smooth, primed surface. The standard industry figure is 350 to 400 square feet per gallon for interior latex paint. However, actual coverage depends on several factors including wall texture, paint quality, application method, and surface porosity. Rolling typically provides more even coverage than brushing for large surfaces. Higher-quality paints with better pigment concentration often cover more area per gallon and may require fewer coats, potentially saving money despite a higher per-gallon price.

Exterior paints generally have lower coverage rates around 250 to 350 square feet per gallon because outdoor surfaces tend to be rougher and more porous. Trim and specialty paints also cover less area because they are applied to smaller, more detailed surfaces where more paint is used per square foot. Always check the specific coverage rate printed on your paint can and adjust the calculator accordingly for the most accurate estimate.