Bottom Line

You need about one gallon of paint for every 350 to 400 square feet of wall, after you subtract doors and windows and multiply by the number of coats. A typical 12 by 14 foot room with 8 foot ceilings, one door, two windows, and two coats needs about two gallons.

How do you calculate how much paint you need?

Start with the perimeter of the room, which is the length of all the walls added end to end. Multiply the perimeter by the ceiling height to get the total wall area. Then subtract 10 square feet for each window and 20 square feet for each door. Multiply what is left by the number of coats you plan to apply, and divide that number by 400. Round up to the next whole gallon.

How many square feet does a gallon of paint cover?

A gallon of paint usually covers 350 to 400 square feet, and a quart covers about 100 square feet. A gallon of primer covers about 200 to 300 square feet, so primer runs out faster than paint. Use 400 in the formula when you want the most optimistic count, and 350 when you want a safer count.

What is a worked example?

Take a room that is 12 feet by 14 feet with 8 foot ceilings. The perimeter is 52 feet, so the wall area is 52 times 8, which is 416 square feet. One door and two windows take away 20 plus 20, which is 40 square feet, leaving 376. Two coats means 752 square feet of coverage. Divided by 400, that is 1.88 gallons, so buy 2 gallons. Divided by 350, it is 2.15 gallons, so a careful painter would buy 2 gallons and a quart.

How much paint do you need for the ceiling and primer?

For the ceiling, multiply its length by its width and divide by 400 to get gallons. For primer, take the wall area you want to prime and divide by 300 to get the minimum gallons for one coat. In the example room, the 12 by 14 foot ceiling is 168 square feet, which is well under one gallon of ceiling paint.

How much extra paint should you buy?

Keep one or two extra quarts for future touch-ups. If you are using a custom color, buy it all at the same time so the shades match evenly. Product requirements also change with the application method and with the surface type and condition, and a textured wall may need a little more than the formula says.

How do contractors use a paint calculator to bid a job?

A gallon count is only half of a bid. Once you know the quantity, you still need the paint cost and the labor to apply it. The TogoMarketing Paint Calculator is a coverage calculator, paint cost, and labor bid tool that works in Excel and Google Sheets for $4.99, with a one-time purchase and no subscription.