The do it yourself resource for homeowners from home improvement professionals.

How to Measure a Door

If you’re ready to replace any door in your home, it’s important to take accurate measurements to avoid order errors. Unless you have access to a truck, your door will likely have to be delivered, so this is a very good time to “measure twice, cut (or order) once” to avoid delays. Here, our door experts share professional insights into how to measure a door and remove interior trim.

Start with Accurate Measurements

Your first step will be to measure the existing door. It should be noted that if you’re replacing an exterior door, it’s a good idea to go ahead and replace the frame along with the door for best fit.

When working out how to measure a door, remember that your existing door will be slightly undersized so it can be opened and closed within the door frame. You’ll want to round the numbers up when ordering your new frame, so a 35 and 3/4-inch-wide door becomes a 36″ wide door purchase. The same rounding up will need to be added to the height.

Other Measurements

You’ll want to pay special attention to the jamb width. This actually refers to the depth of the wall (from inside the house to outside the house) where the door will fit. Getting this right is crucial; if the jamb width is wrong, your trim won’t fit back around the door and you may have issues with weather-tightness.

Rough Opening

You’ll likely need to remove all the interior trim to get an accurate measure of the rough opening. This trim will also need to come out if you plan to add any extra insulation around the door once it’s in place.

When removing interior trim, it’s important to treat it gently.

  1. To save and reuse your trim, you need to avoid splitting it as you pull it off the frame. Carefully insert the flat edge of the wonderbar where the trim meets the wall and tap gently to create a gap.
  2. Work up the gap to pull the trim away from the sheetrock or plaster.
    1. If you have the hand strength, put on a pair of gloves and work the trim with your hands to loosen it.

Once your rough opening is clear, you will know exactly how wide a pre-hung door you can purchase to install in your home.

Final Thoughts

When working out how to measure a door, it’s crucial to be both patient and accurate. Even new houses have challenges, and 90 degrees seldom makes a corner. However, once you’ve got a detailed measurement of the opening, you can purchase a framed door that will successfully fill the gap and provide you with plenty of weather-proof beauty!

Tools & Materials

  • hammer
  • pry bar or wonderbar
  • nail puller (a pair of vise grip pliers works well)
  • patience

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