Estimating Paint Coverage for a Room

Painting Wall 0727

How do I go about estimating paint coverage for this room? There seems to be some confusion about calculating paint coverage for the next painting project. It doesn’t need to be confusing.

1. Estimating Paint Coverage 

The accepted industry standard for paint coverage is 350 – 400 sq. ft. per gallon of paint. This varies because not all paint pigments or colors are opaque. Yellows are very transparent and will require several coats, sometimes as many as three, to match the color chip. Reds and violet-blues are very opaque. Whites are usually opaque, but coverage may vary slightly by the tint base of the white and the underlying color of the wall.

Quality of paint is another variable. Generally, architectural grades of paint have greater coverage capacity. Less expensive paint grades sacrifice opacity and brightness for price. Armed with this information as a basis, let’s get started.

There are several key points to remember. I will use the paint coverage figure of 400 sq. ft. per gallon to make the math simple. But, remember to adjust the figures if using transparent pigmented paint. I recently painted my family room a bright marigold yellow and found it took three coats.

2. Measuring and calculating the gallons needed

A typical interior room 10 ft. by 12 ft. and with 8 ft. high walls is calculated like this.

There are 2 walls 10×8, 2 walls 12×8 and a ceiling measuring 10×12. By calculating the following: 10x8x2=160, 12x8x2=192, 10x12x1=120. So, 160+192+120=472. That means there are 472 sq. ft. of wall and ceiling to cover with paint.

Assuming one-gallon paint covers 400 sq. ft. This will require 1 gallon plus 1 quart for this room. If using the lower coverage of 350 sq. ft. per gallon, this requires 1 gallon plus 2 quarts.

I have not subtracted the square foot coverage for windows and doors. With a little extra math you can get closer to the actual square foot area of the walls. Single doors average 21 sq. ft., while windows average 16 sq. ft. Therefore our room, with one single door and window, would have 37 sq. ft. less (21+16=37) of wall area (one door, one window). French doors (double doors), will average 42 sq. ft. and the same for stacked or multiple windows.

3. Primer is usually needed

Primer is needed for previously colored walls or walls that required repair. Most primers will cover 200 – 300 sq. ft. per gallon. Under painting with primer adds another advantage; it dries with a fine “tooth” to the paint surface, helping the final coat of paint adhere to the surface of walls and ceiling better than without the primer coat.

The typical homeowner will want to paint the trim (base boards, doors and windows) with gloss paint, while most interior walls will be in a flat paint. The exceptions are kitchen and bathroom walls; which will usually be semi-gloss or gloss for ease of periodic cleaning and maintenance.

4. Cleaning and prep

Before painting it is always a good practice to fill all the nail holes, and scrub the walls, ceiling, and trim with an aggressive cleaning solution to remove dirt, smoke and grease from all soon-to-be-painted surfaces. This insures the best adhesion of the new paint.

Check the manufacturer’s specifications for coverage area and surface preparation. Then, adjust your list of how much paint to buy.

Tools you’ll need

Pen or pencil
Paper pad
Tape measure

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