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How to Measure a Door

Tuesday October 22nd, 2019
Whether you’re looking for a new style, better features, or replacing a damaged door, a new door comes with many benefits. To minimize the work involved and to stay in budget, you need to know how to measure a door. 
The kind of door you are thinking of installing does affect what steps you take when measuring.  Hinged door measurements will slightly differ from the measurements you take for sliding doors.

How to Measure a Door in 4 Easy Steps

How to Measure for a Traditional Hinged Door

  1. Measure the Door Slab
  2. Remove the Trim
  3. Measure the Frame Size
  4. Measure the Rough Opening

How to Measure for a Sliding Door

  1. Measure the Door Opening
  2. Measure the Trim
  3. Decide on Overlap
  4. Measure Remaining Space
Measuring a door incorrectly may result in purchasing a door that is too big or too small. A door that doesn’t fit means a lot of extra work, either purchasing another door or cutting the opening to fit the door. All of this will make your project last longer and cost more than expected.

The standard interior door width is 32-inches, and the standard exterior door width is 36-inches. However, you run the risk of getting the wrong size door for your specific opening. Even if it turns out your door opening is a standard size, it's better to know this before you select a new door, rather than find out after that you have the wrong size.

Whether you need to know how to measure for a new door or how to measure a door for replacement, these 4 steps will work for you. Either way, the good news is, that as long as you measure the door correctly, installing a new door is a relatively simple process you can DIY. 

How to Measure for a Traditional Hinged Door

1. Measure the Door Slab

The first thing you’ll want to measure is the door slab. The door slab is the actual door without the frame or hardware. You’ll need to measure the height, width, and thickness of the door. Your new door slab needs to be the same exact size, or at least trimmable to the exact size.

To measure your door, you’ll need to grab your measuring tape so you can get the measurements you need. The process will be the same whether you are measuring for an interior door or an exterior door. Measure the slab from the ‘inside’ which is the side with the hinges.

How to measure a door slab:

To measure your door slab, you’ll want to open the door and measure the actual panel that swings. To ensure you have the most accurate measurements, measure the door slab from the interior side. This means measuring the side of the door slab with the hinges. 
  • Measure the door width. Do this by measuring from the left to the right side of the door. The average door width ranges from 24-inches to 36-inches. Exterior door sizes may even be larger. 
  • Measure the door height. Using your measuring tape, measure from the top of the door to the bottom of the door. The average door height is a minimum of 80-inches. 
  • Measure the thickness of the door. Do this by measuring from the front to the back of the door. The standard door thickness is 1 ¾ inch. 
If you are replacing only the door slab and do not intend to replace the frame, you have all the information you need to select a new door slab.  

If you intend to purchase a prehung door, this means you are replacing the door and the frame, as those two pieces are purchased preassembled.  You will need further measurements to ensure you purchase the right setup. 

2. Remove the Trim

Trim is an added decorative piece to frame the door and gives it a polished and complete look. This means that it is relatively easy to remove. To remove your trim all you’ll need is a pry bar and a bit of patience. If done gently you can reuse the trim without having to replace it. 

When you remove the trim, you’ll be able to see the wooden frame. This will help you make more accurate measurements. You’ll want to remove the trim whether you are measuring for an interior or exterior door. However, note that when you are measuring for an exterior door, you’ll want to remove both the interior trim and the exterior trim. 

3. Measure the Frame Size

Once you know the size of your door slab and you’ve removed the trim, you need to measure the size of the door frame. The door frame is the wooden frame that surrounds the door slab. The hinges for the door slab attach to the frame when hanging the door. 

Measuring the door frame is especially important if you are looking to install a prehung interior or prehung exterior door.  

How to measure a door frame:

Just as with the door slab, several measurements must be taken. You’ll want to stand in the door opening to take the measurements for the door frame. This is true for both interior and exterior doors. 
  • Measure the frame height. When you measure frame height, be sure to do it from the middle of the frame. Do this by measuring from the bottom inside edge of the door frame to the floor. 
  • Measure the frame width. Measure the width of the frame by measuring from the inside edge of the left side to the inside edge of the right side of the frame. Be sure to measure in a few different places and go with the smallest measurement. 
  • Measure the door jamb. This requires measuring the depth wooden frame that holds the door from front to back.

4. Measure the Rough Opening

When you are replacing a door, you need to know exactly how much space you have to work with, so the new frame will fit inside the opening. The best way to figure out how much space you have is to measure the rough opening. 
You can get this measurement by removing the frame entirely. You’ll need the measurement for the rough opening whether you are installing a barn door, a single door, or double doors. 

If you are replacing your exterior door and you have sidelights, you need to decide if you want to keep your existing ones or if you’ll be replacing them. If you decide to keep them, you do not need to include them in your rough opening measurements. However, if you choose to replace them, then you’ll also need to account for the length and width of your sidelights you are replacing. 

How to measure a rough opening: 

Measuring for a rough opening means measuring the entire opening you have in the wall for the door. Before you measure for a rough opening make sure the door slab, trim, and frame have been removed. 
  • Measure the rough opening height. To get the height measurement, you’ll want to stand in the middle of the opening and measure from top to bottom. 
  • Measure the rough opening width. To get the width measurement, you’ll want to measure from one side of the opening to the other. It is helpful to take this in a couple of different places as there can be slight variance with the opening being smaller in some areas and larger in others. 
  • Measure the rough opening depth. Getting the depth measurement of the rough opening is important to make sure the frame you get is not too deep. If the frame is too deep it will protrude from the wall. 

How to Measure for a Sliding Door

Sliding barn doors are a decor trend that is growing in popularity for a number of reasons.  Not only is it a convenient way to enclose a space, it also makes a larger impact on the overall design and aesthetic.

1. Measure the Door Opening

Unlike a traditional hinged door, a sliding door is just covering up an opening, It isn’t supposed to fit snugly inside a frame.  You just need to measure:
  • The opening from side to side to get the width.
  • From top to the floor to get the height.

2. Measure the Trim

If your opening has trim around the outside of it, then you will need to:
  • Measure from the outside edge of the trim to the inside edge.
  • Add that amount to the opening height.
  • Multiply the trim size by 2 and add it to the opening width.

3. Decide on Overlap

A sliding door needs to completely cover the opening, and in order to do that, it needs to overlap the size of the opening (and the trim, if present).  The amount of overlap is entirely up to you, but generally overlap is 2 to 3 inches on all three sides.  Adjust the height and width measurements to take into account your chosen overlap amount. This will be the basis for the size of the rolling door you need.

4. Measure Remaining Space

An important part of measuring for a sliding barn door is making sure that there is enough space for the door to roll completely to one side or the other.Take a measurement of one side or the other of your opening and ensure that the overall width of your sliding door fits inside it.

You also need to check that there is enough space for the barn door hardware between the door and the ceiling above the door opening. Generally, you’ll want at least 6 inches between the top of the door and the ceiling, but there are hardware options for narrower spaces.   

Keep in mind that your door needs about an inch along the bottom to slide easily.You may want to consider installing a guide rail along the bottom for extra stability, and the height of that hardware needs to be taken into consideration.

Tips for Measuring

The entire process to measure a door is relatively simple. However, some tips can help simplify the process even more and there are some things to keep in mind when measuring for replacement doors or new doors. 
  • Take three measurements. For width, measure across at the top, the middle and the bottom.For height, measure from top to bottom at the right, middle and left.  This will help ensure you are getting consistent and accurate measurements.
  • When taking measurements, round down rather than round up. A slightly smaller door will still fit, whereas a larger door is unlikely to fit.
  • The easiest way to note down measurements is with a diagram. You can either draw one yourself. However, printing a photo of your doorway may be an even easier way of noting the measurements. You can draw directly on the picture or diagram. This will help a professional door salesperson find you the perfect size door. 
  • Working with a company dedicated to high-quality doors can simplify the process of how to order a barn door because they will already know exactly what measurements are needed and can give you additional guidance to ensure you get the right sliding door.
  • When measuring double doors or French doors you want to measure the size of each door. To get the total width of the rough opening, you’ll need to add the width of each door together as well as add an additional 2-inches. For the height of the rough opening, you’ll want to add an additional 2 ½ inches. 

How to Measure a Door in 4 Easy Steps

Once you know your door measurements, you can start shopping for a door. This is the fun part of the whole process. You can pick from several door styles and materials. Depending on where your door will be installed you may pick one material over another. Each material has its own benefits when it comes to soundproofing, efficiency, and security. With modern materials, you can even find a high-efficiency glass door or an equally efficient steel door. 

Just make sure to order everything you need to get the job done properly. This includes any necessary hinges, door handles, door hardware, or even barn door headers if you’ve decided to go with a popular barn door style. 
Your door can transform the style of your home. Taking the time to measure correctly can help make sure you get the correct size. The wrong size door can easily cause your project to last longer and cost more than you anticipated. Knowing how to measure a door is arguably the most important step in giving your home an upgraded look with a new door. 
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