How to Measure an Exterior Door Size

Purchasing a new exterior door requires several measurements of the door opening so that a new door will fit in the same space. The door itself may shrink or swell over time and not fit the original measurements. Taking precise measurements enables a homeowner to choose a replacement door that will require little adjustments in order for it to fit in the same opening.

Exterior doors may need replacing due to weathering.
  1. Open the door and go outside. Measure the width inside the doorjamb from side to side including the trim on each side. Take one width measurement at the top, one in the middle and one at the bottom.

  2. Write all three measurements down on paper with a pen marking which measurements they are clearly. The top, middle and bottom measurements are not always the same on a door width.

  3. Measure the width of the door opening from the inside of the house in the same manner. Write down all three measurements accordingly.

  4. Measure the height of the door opening from the bottom of the doorsill to the header at the top of the door opening.

  5. Measure the thickness of the actual old door.

About the Author

Mary Lougee has been writing for over 10 years. She holds a Bachelor's Degree with a major in Management and a double minor in accounting and computer science. She loves writing about careers for busy families as well as family oriented planning, meals and activities for all ages.