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How to Measure an Exterior Door in 4 Steps

Wednesday November 14th, 2018
Measuring an exterior door

Get your tape measure ready!

Replacing your front door can provide your home with several added benefits. For starters, it’ll give your home’s style factor a much-needed refresh, boosting curb appeal. A new front entry door can also be a more energy-efficient alternative, especially if you live in an older home.

One of the nicest things about getting a new front entry door is that you can easily install it yourself in just a few short steps while still achieving a perfect, level and weathertight install. This makes it an ideal DIY project that even a home handiwork novice can do.

In this tutorial, we’ll walk you through the steps for how to measure for a new exterior door, taking you through the process that leads to a clean install. These steps include accounting for door size (Note: If your door has sidelights, that will add just a few more steps), jamb width, rough opening and exterior opening. And remember: measuring at least twice could save you from making possible errors later on. Let’s get started!

Step 1: Determine door dimensions

When beginning to measure for your new exterior door, start by simply measuring the width and height of your old, existing door. Round these measurements up to full inches in order to more easily find the replacement door size.

Step 2: Jot down the jamb width

Next, record your jamb measurements. Make sure when you are measuring these dimensions that you start to measure from the backside of the interior trim to the back side of the exterior trim. You’ll need this jamb width when ordering your new pre-hung door. Why? This will ensure that the interior trim will fit nice and flush with the wall without the need to add extra jamb extensions.

Step 3: Record the rough exterior opening

It’s important to know how much space you’re working with, so measuring the rough opening is important. Make sure you remove the interior trim (gently) to get the most accurate measurements. Start with the opening width between the framing and then proceed by measuring from the top of the opening to the bottom of the sill. You’ll cross-check these measurements with the rough opening requirements of your new door to ensure a proper fit.

Additional steps for sidelights: Measuring your rough opening also applies to measuring for a door with decorative sidelights. If you choose to leave existing sidelights in place, you will not need to include them in your rough opening measurements. However, if you do want to replace your sidelights, follow the same steps above, taking into account the length and width of your sidelights slated for replacement.

(Pro tip: Most standard, pre-hung options include two sidelights, measuring 10 inches each in width and varying to the length of the door or a shorter or longer custom length.)

Step 4: Assess the exterior opening

The last step in measuring for your new entry door is to measure to the outer exterior casings and jot down the dimensions from the top of the trim to the bottom of the sill. Cross check these dimensions with those of a standard pre-hung door with 2-inch-wide molding trim.

From here, you have a few options if the framed door with the standard trim is too small to entirely fill the opening:

  • Option 1: Order a door that offers a wider, flat casing to fill the opening. You can always incorporate decorative molding overtop to match the style of your existing exterior trim.

  • Option 2: Order the door with standard molding and try to fill the gap with additional strips of wood.

  • Option 3: Order the door without exterior molding and craft your own to ensure a flush fit.

Once you’ve written down all your measurements and you’ve checked them twice, you’re now ready to remove your old door and make your way through the steps to install your new front door.

Happy installing!
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