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If you choose to go DIY, here's how to measure your window.
You’re going to measure the jambs at three points: the top, middle and bottom of the window opening. Start by measuring from the surface of the jambs, not the trim strips or parting beads in your window opening. Use the smallest of these three measurements to order your new window.
Next, measure from the top inside surface of the sill of your window opening. Then make three measurements: one at the left side, the center and the right side of the window. Use the smallest of these three height measurements to order your new window.
When you’re measuring depth, just ignore any pulleys or parting strips, since they'll be removed later. There needs to be at least 3 1/4 inches of opening depth between the inside window trim and the outside blind stop strip. This is so there’s enough room for the replacement window.