How to Measure the Inside & Outside of a Replacement Window

Replacement windows are made to fit the specific window openings in your home, so you need to correctly measure those openings to ensure the best fit. You will need to measure every opening that will receive a replacement window---do not measure only one window and assume the rest are the same size. Measure all your windows in the same way, regardless of frame material or style. Follow the steps below to learn the right way to take the measurements.

Tape measure

Instructions

- 1
  Take all measurements from the inside. Double or triple check as necessary. Outside measurements are not necessary for replacement windows.
- 2
  Measure the window diagonally from top to bottom. Repeat for the opposite side. Compare the measurements---if they are not within 1/4 inch, your window is not square and you should consider hiring a professional to help you replace the window.
- 3
  Measure the depth of the window from the outside stop to the inside stop. This measurement should fall between 3 1/4 to 3 1/2 inches.
- 4
  Measure the width of the window between the left and right jambs. Take three measurements: one towards the top, one in the middle and one at the bottom. They should be the same size, but if they aren't, use the smallest measurement.
- 5
  Measure the height of the window between the top jamb and the uppermost part of the window sill. Take one measurement on the left, one in the middle, and one on the right. If they are not the same size, use the smallest measurement.

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