How to Measure

To get the correct measurement for your window opening, you’ll measure three variables: width, height and depth.

Measure the Width

The window jambs are the vertical sides of the window. Measure from jamb to jamb, across the top, middle and bottom of the window opening. If you’re replacing old windows, ignore any trim strips in your old window opening and measure right to the jamb.

Use the smallest of these three measurements for your order.

Measure the Height

The window sills are the horizontal pieces across the top and bottom of the window. Measure from the sill to sill, taking three measurements, one at the left side, one at the center and one at the right side. As with your previous measurement, if you’re replacing old windows, ignore any trim strips in your old window opening and measure right to the jamb.

Use the smallest of these three measurements for your order.

Measure the Depth

Measure from the front of the jamb to the window on each side. Take the same measurement from the sills, as well.

If you’re ordering a vinyl replacement window, ignore any pulleys or trim strips when measuring for depth; they'll be removed when the replacement windows are installed.

Order Your Windows

When ordering your windows, deduct the following from the rough opening:

• minus 1/2-inch off the overall width
• minus 1/2-inch off the overall height

Reducing the window size from the rough opening measurements ensures that the new window will fit inside the rough opening. This will also give you the necessary room to level and square the new window.