How To Measure Exterior Door: 4-Step Guide (Do This!)

Whether your exterior door is damaged or outdated, replacing it can enhance your home’s aesthetic value and safety. The first thing to do before shopping around is to measure the existing door so that you can find a suitable replacement. However, you have to measure more than the slab and jamb. The quick steps below can help you size the exterior door the right way.

How To Measure Exterior Door For Replacement

Many people believe that measuring an exterior door for replacement is as easy as measuring the door slab. However, you also have to consider the hinge and latch recess locations if you want to reuse the existing door frame. Here’s how to measure a prehung exterior door

Things You Will Need: 

  • Measure tape 
  • Paper 
  • Pencil 

1. Measure Exterior Door Slab

The door slab is the first thing to measure if you want to replace your exterior door without replacing the jamb. You must measure the slab’s height and width in three different spots to size the door right. 

  • Height: With the door closed, measure the height from the top of the door to the bottom of the sill, on both sides and in the middle of the door. 
  • Width: Measure the door from side to side at the top, in the middle, and at the bottom.

Measuring in three different spots is crucial because the door might not have the same height or width throughout the slab. This could happen due to an uneven floor (the door bottom might have been trimmed to follow the curves of your floors) or uneven walls.

If you find differences in the height and width measurements, consider the greatest number when shopping for a replacement door. You can always trim the excess material and make the new slab fit into the frame.

In addition to the measurements above, you must also measure the slab thickness. To do this, open the door and measure the thickness in the middle of the door. 

For correct sizing of your exterior door slab, measure the interior side of the door rather than the exterior one. 

2. Measure Exterior Door Jamb Size

The door jamb is the frame holding the hinges to which the door slab is attached on one side and the latch recess on the other side. 

Using a door frame measurement sheet during this stage can help you remember what each number refers to when buying the new door.

For accurate sizing, take the door off the hinges and measure the internal height and width on the interior side of the jamb

3. Measure Existing Hinge And Latch Recess Locations

Knowing the location and size of existing hinges and latch recess is crucial if you don’t want to replace the frame. Take all measurements on the inside of the slab during this step. 

Measure from the top of the slab down to the top of the upper hinge, then repeat for the lower hinge (from the top of the slab to the top of the lower hinge). If your door has more than two hinges, repeat for each hinge. 

Write down these numbers, then measure the height and width of each hinge. They should all have the same size, but if your door is old, you might find slight differences. In this case, you should replace the frame altogether. 

If they have the same size, write down the type of hinges your existing door has: square or radius and their size (generally 1/4″ or 5/8″). 

Measure the location of the latch recess and latch recess size in the same way. 

4. Measure Existing Boring Specs

Most new door slabs come with a pre-drilled handle and deadbolt holes. Even if the door you want to buy doesn’t have pre-drilled holes, you still need these numbers to determine where to bore these slots. 

Simply measure from the top of the slab down to the center of the handle, then from the top of the slab to the center of the deadbolt (or vice versa). 

Take these measurements with you to the home improvement store and measure the door you like before buying to make sure it fits on the existing frame.

How To Measure Exterior Door Rough Opening?

Whether the door slab you like doesn’t fit on your existing frame or you also want to replace the frame for one reason or another, you must measure the rough opening

Simply measure the exterior casing width from stud to stud at three different points (lowest, center, and highest). Then, measure the door casing height from the sill to the top of the opening on each side. Use the smallest number to buy an appropriate frame and door

What Is The Actual Size Of An Exterior Door?

Typically, exterior door rough openings measure 38 ¼” by 82”. However, you may find that your rough-in has a different size. You needn’t worry. Most brands manufacture different size doors, so finding one that fits perfectly should be easy. 

The table below shows the most common sizes of standard and custom exterior doors: 

Exterior door typeDoor size (Width x Height)Recommended rough opening size (Width x Height)
Standard30” x 80”32 ¼” x 82”
Standard 32” x 80”34 ¼” x 82”
Standard (most common)36” x 80”38 ¼” x 82”
Custom32” x 96”34 ¼” x 98”
Custom36” x 96”38 ¼” x 98”

How Do You Read Door Sizes?

Sometimes, you may want to buy an exterior door for new construction, and you can use the floorplan or building blueprints to determine the right size. 

Most engineers, architects, and constructors write down measurements in strings of numbers that may look incomprehensible at first glance. However, figuring out what size they refer to is easy. Typically, you will see interior and exterior door dimensions written down like this: 2868. 

The number refers to the width and height of the door measured in feet and inches. Thus, the size of the door in our example is 2’8” wide by 6’8” high. 

More often than not, the sizes written down on floor plans of new buildings refer to the size of the door slab. However, this rule is not set in stone, and each contractor may refer to the size in a different way or write down the rough opening of your interior and exterior doors. 

The best way to figure out the size is to ask the builder or project manager.


Can I replace an exterior door without replacing the frame?

Yes, you can replace an exterior door without replacing the frame, as long as the new door slab has the hinges and latch located in the same place as your old door. Otherwise, you’ll have to replace the entire door and frame structure. 

What does a prehung door mean?

Prehung doors are doors sold with everything you need to install them, including a door slab and hinges attached to a three-sided frame. 

How long does it take to replace an exterior door?

It generally takes between five and six hours to remove an old exterior door and replace it with a new one. The actual time depends on the level of expertise and the type of door.


Measuring an exterior door for replacement isn’t complicated, but you must follow the steps above to ensure that each measurement is taken correctly. Otherwise, you might buy a door that doesn’t fit correctly onto the existing frame or that is too large or too big compared to your rough opening. We hope this guide can help you size your exterior door correctly.

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