How to Measure for a New Window in a Cinder Block Opening

Raise the bottom sash of the window halfway up. Hold your tape measure across the opening widthwise, inside the track where the sash was, near the bottom. Write the down measurement on a piece of paper.

Lower the top sash. Measure across the opening at the top, again putting the tape in the track where the sash was. Record the measurement.

Take a third horizontal measurement, as close to the middle of the opening as you can get without the sashes being in the way. (The position will actually be just above the middle.)

Circle the smallest of the three measurements you took (if there is any variation) on the piece to the paper. This is your width measurement.

Put both window sashes at the middle position in the opening, so you can access the top and bottom inside tracks, measuring vertically. The tape measure will span across the fronts of the sashes. Take three measurements, one on the left side, one to the right and one up the middle. Circle the smallest of the three measurements on your piece of paper if there is any variation. This is your height reading.

Order your new window with the height and width readings you circled. Specify to your window manufacturer that this is the base reading for the opening and hasn’t been adjusted. The manufacturer will take 1/2 inch off those figures when making the window, to allow room for adjustment. Leave the old windows in place until the new ones arrive.