Measure the rooms you need to paint, including the door and window size.
All measurements should be in FEET.
One gallon covers about 400 square feet.
Use your figures in the following calculations to measure interior and exterior square footage:
A. Walls
Width (of all walls added together) X height of walls = A (square feet) total wall surface
B. Windows
Height of window X width of window X number of windows = B (square feet) total window surface
C. Doors
Height of door X width of door X number of doors = C (square feet) total door surface
D. Gables
Height X width divided by 2 = D (square feet)
E. Eaves
Width of overhang X length = E (square feet)
A + D + E – (B + C) divided by 400 square feet per gallon = number of gallons you need.