You’ll need: a tape measure, a pencil, and five minutes per window. Measure from inside the house. For replacement insert windows you measure the existing window frame, not the wall opening.
Width — measure three times
- Measure the width at the top, middle and bottom of the frame, jamb to jamb (where the sashes slide).
- Write down the smallest of the three numbers, to the nearest 1/8″.
Height — measure three times
- Measure the height on the left, center and right, from the head jamb down to the sloped sill (the highest point of the sill).
- Write down the smallest of the three numbers, to the nearest 1/8″.
Enter the opening size — we handle the deduction
Enter your smallest width and height in the configurator exactly as measured. The factory makes the standard manufacturing allowance so your new window fits and squares correctly. Don’t subtract anything yourself.
Good to know
- Order width × height — width always comes first in the window industry.
- Tempered glass is required by code when glass is within 24″ of a door, less than 18″ from the floor, near tubs/showers, or on stairs. It’s a checkbox in the configurator.
- Not confident? Order anyway — a specialist reviews every measurement with you before production, and you aren’t charged until then.