It may help to ask a friend to hold the measuring tape in place while you pull it across the wall.

You may need to use a stepstool or ladder to measure the entire height of the wall. Don’t be afraid to ask a friend for help if you need it! All of your height measurements might be the same, depending on the size and shape of your room. Don’t include the trim in your measurements—you’ll be calculating that separately.

For example, if a wall is 15 ft (4. 6 m) and 10 ft (3. 0 m) tall, the total surface area would be 150 ft (46 m).

If all of your windows and doors are the same size, you only need to measure them once—but you still need to multiply by the total number of structures that you have. For example, if you have 3 windows that have a total surface area of 17 sq ft (1. 6 m2), you’d multiply that by 3 (giving you a total of 51 sq ft (4. 7 m2)).

If your total wall surface area is 650 sq ft (60 m2) and you plan on adding 3 coats of paint, you’d need enough paint for 1,950 sq ft (181 m2) of wall space. You may need extra coats of paint if you’re repainting dark walls with light-colored paint.

Paint Calculation Formula: Surface Area / 350 = gallons of paint needed or Surface Area / 400 = gallons of paint needed If you’d rather err on the side of caution, divide your total square footage by 350 rather than 400. That way, you’ll have a little extra paint on hand if the project ends up being bigger than you expect. If you have 1,600 sq ft (150 m2) of wall space to paint, you’d need 4 to 4. 75 US gal (15. 1 to 18. 0 L) to paint your space. If your walls are textured or completely unpainted, divide your total square footage by 250 sq ft (23 m2) instead. These surfaces tend to use more paint than regular, smooth walls.

If you need 4. 44 US gal (16. 8 L) of paint to cover your wall space, you’d round it up to 4. 5 US gal (17 L) instead.

Let’s say the sections of trim are 30 sq ft (2. 8 m2), 40 sq ft (3. 7 m2), 60 sq ft (5. 6 m2), and 25 sq ft (2. 3 m2). The total square footage would 155 sq ft (14. 4 m2); divided by 400, you’d get 0. 38 US gal (1. 4 L). To be safe, you’d round up to 0. 5, giving you a total of 0. 5 US gal (1. 9 L).