Fortunately underbuying or overbuying is easily avoidable. It just requires a bit of measuring and some basic math before you head out to purchase the paint. Here’s how you can answer the question, “How much paint do I need?”
Once you know the coverage rate of your chosen paint, you need to calculate the square footage of the walls or ceilings to be painted. To get this figure, simply multiply the width by the height (for walls) or the length by the width (for ceilings). You then need to subtract the area of anything within the plane that is not being painted, such as windows and doors.
1. Multiply the width and height of the wall:
25 x 10 = 250 square feet
2. Multiply the width and height of the door:
3 x 7 = 21 square feet
3. Subtract the door opening from the area of the wall:
250 square feet – 21 square feet = 229 square feet
4. Divide this figure by the estimated square footage coverage amount of your paint. In this example, let’s say the coverage is 350 square feet per gallon:
229 ÷ 350 = 0.65
5. Round up to the nearest whole number to get the number of gallons needed. In this example, you’d round up to 1 gallon, to apply one coat of paint.
Note: If you need to apply two coats, you simply double the square footage to be painted and then divide by the coverage:
458 ÷ 350 = 1.31
(Here, you’d round up to 2, so 2 gallons of paint would be needed to apply two coats.)
1. Add together the width of each wall to be painted:
12 + 20 + 12 + 20 = 64 feet
2. Multiply this sum by the height of the walls:
64 x 8 = 512 square feet
3. Multiply the width and height of the door:
6 x 7 = 42 square feet
4. Subtract the door openings from the area of the wall:
512 square feet – 42 square feet = 470 square feet
5. Divide this figure by the estimated square footage coverage of our paint. Again, in this example, we are going with 350 square feet per gallon:
470 ÷ 350 = 1.34
6. Round up to the nearest whole number, in this case 2. You would need 2 gallons to paint one coat.
Note: Again, for two coats of paint, you double the square footage to be painted:
470 + 470 = 940
Then divide by the coverage per gallon:
940 ÷ 350 = 2.69
(Round up to 3. You would need 3 gallons of paint to apply two coats.)
The quality of your paint will also affect the amount you need. Higher quality paint tends to offer better coverage, requiring fewer coats, whereas a lower-cost paint may be thinner and therefore require more coats for proper coverage.
Also, it’s a good idea to keep a record of the paint brand, colors and sheens you used, so if you need to touch anything up down the road you know exactly what you need.