Estimating How Much Paint to Buy for Walls
Estimating how much paint to buy is important whether you paint an entire room or a single wall. Estimating paint depends on the amount of wall you want to cover and how coarse the wall is. Make sure that you have the right amount of paint because the only way to ensure your color stays consistent is to purchase all your paint at the same time.
You get what you pay for. You might be better off spending a bit more per gallon of paint than buying the cheapest paint available, which will require you to paint more coats and, ultimately purchase more gallons, to get good coverage.
You usually can’t return unused cans of custom-mixed paint, so if you buy too many, you're stuck with it. On the other hand, you'll have a steady supply for touch ups. The more accurately you can estimate how much paint you need, the less likely you are to end up with too much, or too little, paint.
Add together the length of each wall.
[wall] + [wall] + [wall] + [wall] = wall length
For example, 16 + 16 + 20 + 20 = 72 feet.
Multiply the total length of walls by the total height.
72 feet x 9 feet = 648 square feet
Subtract 20 square feet per door and 15 square feet per window.
[wall] - [door] - [window] = square footage
For example, 648 – 20 – 20 – 20 – 15 – 15 – 15 – 15 = 528 square feet.
Divide the answer by 350 (the estimated coverage/gallon) for smooth walls; or divide by 300 for rough or textured walls, which soak up more paint.
[square footage] ÷ 350 = 1.5 gallons for smooth walls per coat
For example, 528 ÷ 350 = 1.5 gallons for smooth walls and 528 ÷ 300 = 1.76 gallons for rough/textured walls.
Add 10 percent for waste.
1.428 x .10 = 0.1428
1.428 + 0.1428 = 1.57or 2 gallons for each coat of paint.
Between paint drying in the pan and mistakes along the way, you'll want to have this 10 percent cushion. After all, you don't want to run out.