Prehung Door Rough Opening: What Is the Correct Size?

A small house made of sticks next to a hammer and a tape measure.

Before you choose your new pre-hung door, it's important you know the size of the opening. Getting the right size door for the opening helps to make your installation smooth and will eliminate having problems down the road.

Pre-Hung Door Measurements

Measure the opening to your door frame. Be sure to allow for about a 1½ inch larger opening than the standard door sizes. Typically a pre-hung door is measured in 30-inch and 36-inch sizes with additional sizes available in non-standard widths.

The doors are also a standard 80 inches tall. Presuming the door is a 36-inch wide door, the dimensions of your opening should be 37½ inch wide by 81½ inch tall.

Reasons for Door Opening Sizing

When a pre-hung door is being installed into an opening there have to be considerations for leveling the door, and ensuring that it has an obstruction free swing. If the pre-hung door is butted up into an opening, the swing will be hindered by the door. It may scrape the floor or it may get stuck as it is closing.

An opening that is the same size as the frame on the pre-hung door can alter the shape of the frame and make the installation more difficult.

Taking the guesswork out of choosing the correct size pre-hung door makes things much easier. Now that you have the know-how, you're all set to head to the hardware store.

Prehung Door Rough Opening FAQ

What is the rough opening for a 32 by 80 inch door?

The rough opening for the door will be entirely determined by the size of the door. You will need to add about 2 inches to the width of the door and 2 1/2 inches to the height to determine how big the rough opening should be.

So for example, if your door is 32 inches wide, the rough opening should be 34 inches wide. If the door is 80 inches tall, make the rough opening 82 1/2 inches tall.

How can you determine the rough opening size required for a door?

As a general rule, you want to add two inches to the width of the door and two and a half inches to the height of the door to create an opening big enough for the door rough.

However, there are many rough door opening size charts online that totally take the guesswork out of determining your rough size. All you have to do is find the size of your door on the chart, and you can see exactly how big the rough opening should be.

Is a 32 inch door too small?

The most standard size for interior doors in residential homes is 32 inches. This is the most common door size, so it should feel comfortable and pretty standard if you install a door of this size in your home.

How much gap do you need to leave when framing a door?

The gap between the frame and door is small, but it definitely needs to be there. When a door is finished and hung, there should be two to three mm of space between the door and the frame.

This gap allows the door to swing and move freely.

Is a 32 door actually 32 wide?

A 32-inch door is actually only 32 inches wide when you factor in the frame and the door. The door will be up to one inch shorter than the advertised size because of the frame.