Measuring for an interior door

By Masonite

Knowing how to measure for your new interior doors is an important first step in any replacement project.

A sitting room featuring a 5 panel light teal interior door, white table and dresser and plants on the windowsill

Are you ready to revamp the look and feel of your home’s interior? Upgrading your interior doors can make a significant impact on the overall aesthetic and functionality of your living spaces, and it’s a project you can take on that will pay off. Whether you want to swap out an old or damaged door, change your home’s style or upgrade to solid core doors to help manage sound in your home, a new interior door can be transformative. 
Before getting started, it’s important to understand how to accurately measure for a new interior door so you can purchase the right door for your space and have optimal functionality. Read on to learn the steps to take to confidently complete this part of your project.

How to measure for an interior door

How to measure for an interior door

When it’s time for a new door, you have the option of either a prehung door or a slab. Prehung doors include a slab with hinges already attached to the frame for easy installation, while a slab is just the door. Follow these steps to measure for a new flat jamb prehung interior door: 

1. Gather your safety equipment, tools and materials

You’ll need the following to get started: 

  • Utility knife
  • Flat pry bar
  • Wide putty knife
  • Tape measure
  • Safety glasses
  • Safety gloves
  • Something to record the measurement

2. Remove the door casing

Door casing is the trim found around the door opening. Here is how to remove this piece of your door: 

  • Wearing the safety glasses and gloves, use a utility knife to cut all the way around the door casing on the side of the door with the hinges showing.
  • Starting at the top corner, insert a wide putty knife between the casing and the wall to create separation.
  • Insert a pry bar or the claw of a hammer between the putty knife and the casing, applying pressure to the pry bar to pull the casing away from the wall.
  • Gradually work your way down until the casing comes off the wall, being cautious of any nails or staples. This will expose the rough opening, which is the structural frame that surrounds the door unit. Take extra care with this step if you plan to reuse the casing.

3. Measure the rough opening

Rough opening sizes can vary, so it’s important to measure yours accurately to ensure you’re buying the right door for your space. Follow these steps to measure this area: 

  • With a tape measure, obtain the measurement across the rough opening to determine its width. Do this three times: once across the center, and once each on the top and bottom edges to ensure accuracy.
  • Be sure to record the smallest of your three measurements down to the nearest 1/16”.
  • Measure the rough opening height, from the finished floor or carpet up to the bottom of the header framing. Do this three times: once across the center and once on each side.
  • Again, record the smallest measurement down to the nearest 1/16”. 

4. Obtain the side jamb depth 

The next step in measuring for your interior door involves getting the size of the side jambs (the vertical parts of the door frame that connect to the head jamb) to ensure the door unit will fit into the wall.  
To do so, measure from the interior wall to the exterior wall, again to the nearest 1/16”. Common side jamb measurements are 4 and 9/16”, 5 and ¼”, or 6 and 9/16” 
With the rough opening width, rough opening height and side jamb depth, you have the measurements you need to determine which door unit will fit your home. 

5. Determine the door handing and swing

To figure out your door’s handing and swing, open your door and stand in the doorway with your back to the door’s hinges. Reach out to grab the door’s handle. If it’s on your right, it’s a right-hand door. If it’s on your left, it’s a left-hand door. 
What type of swing door you have depends on how it opens. If the door opens into the room you are entering, it is an inswing door. If it opens out, it’s an outswing door. 
So, you can have a left hand reverse swing (if your door’s hardware is on the right and you pull the door open from the outside of the room), a right hand reverse swing (if your door’s hardware is on the left and you pull the door open from the outside of the room), a left hand swing (if your door’s hardware is on the right and you open the door into a room) or a right hand swing (if your door’s hardware is on the left and you open the door into a room).

Handing and swing

Interior door replacement options 

When it comes to replacing your interior doors, Masonite offers a wide range of choices that combine design and durability. Regardless of your architectural style, you can find Masonite interior doors that match. 
Whether you’re aiming for a traditional, contemporary or rustic look, you can customize your interior spaces by choosing from barn, French, flush and molded options. Our solid core flush and molded doors are engineered to withstand wear and tear, ensuring long-term performance. With a focus on quality craftsmanship, Masonite doors are built to resist warping, shrinking and expanding, ensuring a proper fit and smooth operation for years to come. 

Last Updated: July 03, 2023