How to Calculate Gallons of Paint Needed (Interior Painting)

When remodeling the interior of your home, getting an accurate paint estimate can save you the time and trouble of heading back to the home improvement store for more paint. It will also save you money, since good estimates keep you from buying too much paint! If you need a room by room estimate of number of gallons of paint needed, use the simple formulas below.

Things You'll Need

• paper, pencil, calculator

Instructions

1. First, compute the total area of the windows and doors in the room by multiplying the width and length of each window and door. Call the total area of windows and doors "D."

   For example, if a room has two 2.5 by 6 foot doors, and one 3 by 3 window, then

   D = (2.5)(6)+(2.5)(6)+(3)(3)
   = 15+15+9
   = 39 sq. ft.

2. Next, calculate the wall area with the formula 2H(L+W), where "H" is the height of the walls, "L" is the length of the room, and "W" is the width of the room.

   For example, if a room is 12 by 12 feet with a height of 8 feet, then

   2H(L+W) = 2(8)(12+12)
   = 384 sq. ft.

3. Now calculate the total paintable wall area with the equation

   2H(L+W) - D.

   In our example, 2H(L+W) - D = 384 - 39 = 345 sq. ft.

4. Assuming that one gallon of paint covers 300 square feet, and that the walls of the room need two coats of paint, take the number you obtained in Step 3, and multiply it by 0.00667

   Using our example, (345)(0.00667) = 2.3. So the walls need 2.3 gallons of paint.

5. Lastly get an estimate for the amount of paint needed to coat the ceiling. Assuming that a ceiling needs one coat of paint, the ceiling estimate is given by the formula 0.00333LW.

   In our example, L = W = 12, so the number of gallons needed to paint the ceiling is (0.00333)(12)(12) = 0.48 gallons.

   The total amount of paint needed for this room is 2.3 + 0.48 = 2.78 gallons.

6. The complete formula for gallons of paint needed is

   (0.01333)H(L+W) - (0.00667)D + (0.00333)LW