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Sizes and Measure: A Guide to Interior Door Rough Opening

Whether it be an exterior or an interior door rough opening, getting the accurate measurement of your door saves you plenty of time and energy during installation. Because admit it or not, a lot of homeowners fail to do it correctly.

But it is not necessarily because they do not know how to do it. It is just the task is quite demanding, particularly that rough openings’ measurement for all types of doors—both interior and exterior—varies.

That said, before you purchase that interior door you are eyeing, learn how to measure the rough opening accurately first.

Standard sizes for Interior Door Rough Opening

The size of a rough opening varies depending on the type of door.

Take the size of exterior and interior door rough opening as an example. While the standard size for both rough openings’ width is the same, some vary in height due to the manufacturer’s standard production. Rough openings for a typical interior door are the same as well but may also vary depending on the type—if it is an atrium, a slider, or a French door.

Apart from that, an interior door rough opening is slightly larger and wider compared to the rough opening of an exterior door too. The measurement may also differ, especially if the door is customized.

How to measure indoor door rough opening?

Does the explanation above sound complicated? I bet it does. 

Look at this simple chart guide. 

Type of doorWidthHeight

Single door

Add 2” to door width

Add 2 ½“ to door height

Double door unit

Add 2” to door width

Add 2 ½” to door height

Double door unit with astragal 

Add 2 ½” to door width

Add 2 ½” to door height


French door

Multiply the width by 2 then and 2”


Add 2 1/2 “

As shown above, there is a simple formula to accurately measure a door rough opening for each door type. And to put things in perspective, below is a brief explanation of how to calculate an interior door’s rough opening:

  • Single door. A single door rough opening is 2” wider and 2 ½” taller than the actual door size. Thus, if, say, your single door’s size is 2/6 x 6/8, then the rough opening is 32” wide and 82 ½” tall.
  • Double door unit. The same formula used for a single door—which is by adding a 2” allowance for width, and a 2 ½” allowance for height—applies to a double door unit as well.
  • Double door unit with astragal. On the one hand, for a double door unit with astragal, you have to add 2 ½” in width and height. Hence, if you have a double door unit with an astragal in the size of 5/0 x 6/8, then the rough opening is 62 ½” wide and 82 ½” tall.  
  • French door. On the flip side, however, calculating a French door rough opening is slightly different. To get an accurate measurement, you must multiply the door’s width by 2″ and then add 2”. For the height, simply add 2 1/2“. So, if you have a 30 inches wide and 80 inches tall French door, then its rough opening is 62 inches wide and 82 ½ inches tall.
  • Sliding door. Unlike the four doors mentioned above, measuring a sliding door’s rough opening needs no formula. You can instead manually measure it using a measuring device.

    To get the width, run a tape measure across the door, stud to stud. Then get the height by placing a tape measure between the seal or the bottom and the head jamb.

Standard Sizes for Doors

Getting the right measurement of rough openings is easier if you know the basic and standard sizes of doors. So, now that you know how to measure an interior door rough opening, let’s discuss door measurement and sizes for a bit.

Here are the standard width and height of a door: 

  • Door width. A door’s width comes in three sizes: 2/6 (30”), 2/8 (32”), and 3/0 (36”). These are considered the standard measurements.
  • Door height. Standard door height comes in two sizes only: 6/6 (78”) and 6/8 (80”). 

How to measure a door?

To get the size of a rough opening, you must measure the door’s actual size first. Here is a quick guide to help you:

Step 1: Start with the height

Starting from the top corner to the bottom corner, simply run a tape measure along with your door. Keep in mind to measure the door only. You may also need to measure more than one spot of your door, specifically for older ones. And if the measurements vary, choose the highest number.

Step 2: Measure the width

To measure the width of a door, simply run a measuring device across the door, from the left corner to the right corner. Make sure that you are measuring the door only, and no other elements like weather-stripping are included. 

On the one hand, if the door is old and worn out, make sure to measure more than one spot. Tattered doors are not perfectly rectangular, and may give you wrong measurements. And if, say, the sizes are not similar, take the highest number.

Step 3: Measure the door’s thickness

To get a door’s thickness, simply hold a tape measure on the edge of the door. It is also better to measure the edge of the door frame, also known as the jamb. If you feel unsure, the common thickness of a door is 4.4cm or 1.75 inches. 

Measuring a Rough Opening is Simple

Measuring the exterior or interior door rough opening (though quite challenging) is easy if you know the basics well. On the one hand, that does not mean you would not need a professional to help you with—unless you are an expert yourself.

So, do not hesitate to reach out to a team of home building and improvement professionals, especially if you are unsure. They can help you with anything, from taking the right measurements to door installation.

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