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How to Measure a Door: 3 Different Door Types

Are you measuring for your new door the right way? Double-check with these tips.

Have you ever wanted to replace a door yourself but had no idea where to begin? I’ll show you how to measure a door the easiest possible way.

You’ll learn how to read height, width, length, and thickness correctly, and where to place your measuring tape. Who needs to pay for a professional when you can DIY?

Key Takeaways

  • Know the door’s anatomy, such as casing, panels, stiles, and rough opening.
  • Understand the difference between pre-hung doors and door slabs.
  • Measure the width, height, and thickness of the door and frame for accurate sizing.
  • Consider the door’s swing direction for ease of access and functionality.

Anatomy of a Door

Before learning how to measure a door, it’s essential to know the terminology involved.

  • Casing: Also known as a frame, usually built into the wall.
  • Panels: Door’s main surface; can have single or multiple panels.
  • Stiles: Sides of the door, which act like door panel frames.
  • Hinge Stile: The stile (side of the door) that will have the hinges.
  • Rough Opening: The door gap that holds the frame.
  • Header: Top part of the door.
  • Jamb: Interior part of the door, located on either side.
  • Trim: Decorative section that covers the door frame.
  • Sill: Bottom part of the door, located below the header.
  • Mullion: Door division that splits the door into two equal parts.

Pre-Hung Door vs. Door Slab

A slab door is a simple, unframed door. As it doesn’t come with a frame, you need to attach the door slab to an existing door frame or create an entirely new door frame.

Pre-hung doors are door slabs with a pre-installed door frame. They are available as complete kits, but some of them have features that you have to install by yourself.

How to Measure For a Door Slab

Grab your measuring tape!

1. Measure the Width

The first step in learning how to measure door size is grabbing your tape measure. Place it on the door and measure the distance between the top left and the top right side of the door.

Repeat the measurement for the middle section of the door. If the resulting numbers are different, use the highest one as the door’s width.

2. Measure the Height

Repeat the measurement process, but this time from the top corner to the bottom corner. Do this vertical measurement once more, but measure the slab in a different area the second time. If you get two different measurements, use the longest one.

3. Measure the Thickness

With the door opened, measure the thickness of the door. Alternatively, you can measure the distance between the jamb’s backside and stops.

4. Measure the Frame

Use your tape measure on the door frame’s interior side and measure from one side to the other. If you measure in multiple locations, use the smallest measurement as the width of the frame.

To measure the height of the door, measure the distance between the upper trim’s lowest part and the floor. Measure the distance between the side frame’s outer area and the inner part for the thickness.

Pro Tip

It’s always best to take multiple measurements of the same door part for a more accurate idea of what you’ll need.

How to Measure For a Pre-Hung Door

The following tutorial addresses how to measure for a door in a rough opening.

1. Measure the Width

Start by placing the tape measure on the inner stud (2×4) on one side and extending it to the stud on the other side. Take multiple measurements in different locations and use the lowest number as the width.

2. Measure the Height

Using your measuring tape, determine the distance between the header’s lower part and the floor. Take three different measurements and consider the smallest one as the height.

3. Measure the Thickness

Since there is no door slab here, you can measure the actual thickness of the wall.

How to Measure For a Sliding Door

Sliding doors can be tricky. Instead of allowing for hinges or swinging doors, you must ensure a tight fit. But with these tips and steps, you can do it like a pro.

1. Measure the Rough Opening Width

Grab your tape measure and use it to determine the distance between one stud to another. This will tell you the rough opening size for the sliding door. It should be about half an inch larger than the door itself.

2. Measure the Rough Opening Height

To measure the rough height, determine the distance between the top and bottom of the opening. Measure at the center, far left, and far right, and use the smallest measurement to establish the door height. It should be half an inch bigger than the door.

3. Measure the Thickness

Record the measurement of the jamb without the trim. You need the distance from one edge to another from the existing door frame.

Which Way Does the Door Swing?

It is essential to determine which way you need the door to swing open when acquiring a door. If the swing direction is incorrect, this could prevent easy access to the room or result in a blocked or cramped area.

Most doors open inwards. For interior doors, this is because you don’t want the door opening out into a high-traffic area such as a passage. For exterior doors, it’s due to security reasons and prevents your door from being affected by adverse weather.

There are, of course, exceptions to the rule, which include screen, storm, and fire doors that open outwards. Or perhaps you simply have an obstruction such as a pillar in the way.


Measuring a door might seem like a simple task. But I get these questions all the time.

What are the Standard Door Sizes?

All passage doors must be at least 80 inches tall, and conventional interior door widths are 24 inches, 28 inches, 30 inches, 32 inches, and 36 inches. The suggested minimum door width for easy access for wheelchair users is 36 inches.

How Do You Read a Door Size?

A door could have its size written as 3680, but what does that mean? The first digit represents the width in feet, while the second digit represents the additional inches. The third number is the height in feet, and the last digit is the additional inches.

In this instance, 36 is the equivalent of 3 foot 6 inches and refers to the door’s width. 80 is equal to 8 feet and is the door’s height. The size could also be written as 36 x 80, with the same outcome as the above example.

Is It Easy to Replace a Door?

It’s almost as simple as it sounds to replace an existing door with a new one. The old door serves as a template for cutting the new door to size and equipping it with a lockset and hinges. Then you replace it in the jamb that already exists.

Can I Replace a Door Without Replacing the Frame?

A door can be replaced without replacing the frame, provided the frame is in excellent condition and not deformed or damaged. Before doing so, make sure to check our guide on how to measure the door size.

How Do You Measure For a Storm Door?

Ensure that you measure from the location of the storm door, not the location of your front entry. Measure the height from the top to the bottom of the threshold. For the width, measure from the left to the right side of the mold where you’re going to mount the door.

Bottom Line

Now that you know how to measure a door, all you need is a pencil, paper, and some measuring tape. Measuring door sizes is the least complicated part of choosing to install a new door.

Whether you’re looking for a replacement door or want to install one where no door has gone before, this guide will help you.

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About the Author

Candace Osmond

Candace Osmond is a USA TODAY Bestselling Author and Award-Winning Interior Designer. Using her years of hands-on experience, she now writes about design and DIY. She currently resides on the rocky East Coast of Canada with her family and slobbery bulldog.