Most replacement windows are manufactured in 1/8" increments.
Example Width
27-1/8", 27-1/4", 27-3/8", 27-1/2", 27-5/8", 27-3/4", 27-7/8"
Example Height
52-1/8", 52-1/4", 52-3/8", 52-1/2", 52-5/8", 52-3/4", 52-7/8"
Overall depth of window is 3-1/4".
Height: From the inside of the house, measure between inside sill, and top of window in back of the inside of the inside stop. Measure both the left and right side.
Use the smallest measurement.
See diagram to the right.
Width: Measure between jambs at three points; top middle, and bottom. In front of the inside stop. Use smallest measurement.
See diagram below.
For more instructions, see our page on installing a replacement window.