Paint Calculator

How to Use the Paint Calculator

The Paint Calculator helps you estimate the amount of paint needed to cover the walls of a room. Whether you are refreshing a single bedroom or painting an entire home, accurate paint estimation saves money by preventing over-buying and avoids the frustration of running out mid-project. Simply enter your room dimensions, specify doors and windows, and get a precise gallon estimate.

Entering Room Dimensions

Start by measuring the length and width of the room in feet. The calculator uses these measurements to compute the total wall perimeter (2 x length + 2 x width). Next, enter the wall height, which defaults to the standard 8 feet for most homes. If you have vaulted ceilings or taller walls, adjust this value accordingly. The total wall area is calculated by multiplying the perimeter by the wall height.

Accounting for Doors and Windows

Doors and windows reduce the paintable surface area. The calculator uses standard sizes: 21 square feet per door (a standard 3 x 7 ft interior door) and 15 square feet per window (a standard 3 x 5 ft window). Enter the number of each, and the calculator subtracts the total door and window area from the gross wall area. If your doors or windows are significantly larger or smaller than standard, you can adjust the count to approximate the actual area difference.

Choosing the Right Number of Coats

Two coats of paint are the industry standard for most interior painting projects. This ensures even color, proper hiding of the old surface, and good durability. You may get by with a single coat when repainting with the same or very similar color. Three coats are sometimes necessary when painting over very dark walls with a light color, or when using paints with lower hiding power such as bright reds, deep yellows, or certain organic pigments.

Understanding Paint Coverage Rates

The default coverage rate is 350 square feet per gallon, which represents a typical interior latex paint applied to smooth, primed drywall. Premium paints may cover 350 to 400 square feet per gallon, while budget paints or highly textured surfaces might only achieve 250 to 300 square feet per gallon. Adjust the coverage field based on the paint manufacturer's recommendations found on the can label.

Types of Interior Paint

Flat or matte finishes hide imperfections well and are ideal for ceilings and low-traffic areas. Eggshell offers a slight sheen with good washability, making it the most popular choice for living rooms and bedrooms. Satin provides a smooth, velvety finish that resists moisture, suitable for kitchens and bathrooms. Semi-gloss and high-gloss finishes are durable and easy to clean, commonly used on trim, doors, and cabinets. The finish you choose does not significantly affect coverage rates.

Surface Preparation Tips

Proper surface preparation is essential for a professional-looking result. Clean walls with a damp cloth to remove dust and grease. Fill nail holes, cracks, and dents with spackling compound and sand smooth once dry. Lightly sand glossy surfaces with 150-grit sandpaper to improve adhesion. Apply painter's tape along edges, trim, and ceilings for clean lines. Use drop cloths to protect floors and furniture from drips and splatters.

When to Use Primer

Apply a separate primer coat when painting new drywall, covering stains or water damage, switching from oil-based to latex paint, or making a drastic color change (especially dark to light). Primer seals the surface, improves adhesion, and can save you an additional coat of expensive topcoat paint. Many modern paints include built-in primer that works well for routine repaints over previously painted walls in good condition.

Frequently Asked Questions

Q: How much area does one gallon of paint cover?

A: One gallon of paint typically covers about 350 to 400 square feet of smooth, primed wall surface with a single coat. Coverage varies depending on the paint quality, surface texture, and application method. Rough or textured surfaces, porous drywall, and dark-to-light color changes can reduce coverage to 250-300 square feet per gallon.

Q: Do I need to apply primer before painting?

A: Primer is recommended when painting over new drywall, covering dark colors with a lighter shade, painting over stains or patches, or switching between paint types (e.g., oil-based to latex). Many modern paints include built-in primer (paint-and-primer-in-one), which works well for repainting walls already in good condition with a similar color.

Q: How many coats of paint should I apply?

A: Two coats of paint are standard for most interior walls. This ensures even coverage, true color, and good durability. A single coat may suffice when repainting with the same or very similar color. Three coats may be needed when covering very dark colors with a light shade or when using certain reds, yellows, or bright colors that have lower hiding power.