Measuring for an exterior door

By Masonite

Upgrading your front door starts at obtaining accurate measurements of the space.

A close-up of a porch on a white shingled home with a wood-looking front door that has 5 equal lite glass panels and two sidelites

Wanting to replace your existing front door? Upgrading your existing door can do a lot of things, from enhancing your home’s curb appeal to increasing energy efficiency, so this kind of project does come with significant advantages.  
Understanding more about the project is necessary before you begin, starting with knowing how to get accurate measurements. With the right measurements, you can confidently select the right door size, ensure a proper fit and experience a smooth door installation process. 
In this article, we’ll walk you through the step-by-step process of measuring for a new exterior door. From taking exact measurements of the door frame to considering factors such as clearance and door swing, you will have the knowledge you need to measure for an exterior door and make your home improvement project a success. 

How to measure for an exterior door

Accurate measuring of the rough opening is how you’ll know what size door unit will fit in your home. The rough opening is the structural frame that surrounds the door unit. 
To perform this work, you’ll need a utility knife, a pry bar or hammer, a tape measure, a wide putty knife, a pencil and a piece of paper, safety glasses and safety gloves. Also, make sure to note which side the door hinges are on and the direction the door opens. 

Then, follow these steps to measure for a new front door:

Step 1: Remove the interior door casing

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

  • Standing on the inside of your house, cut all the way around the interior door casing using a utility knife.


  • Starting at the top corner of the door casing, insert a wide putty knife between the door casing and the wall to create separation.


  • Insert the pry bar or the claw of a hammer between the putty knife and the door casing. Apply pressure to the pry bar to pull the door casing away from the wall, being cautious of any nails or staples.


  • Gradually work your way down the door casing until it comes off the wall.
  • Repeat this on the other side of the unit, as well as on the top.


2. Obtain the rough opening dimensions

Common rough opening widths are 38.5” and 34.5.” And common heights are 82.5” and 98.5,” but rough opening sizes can vary. It’s important that you measure down to the fraction of an inch and write down the smallest dimension of your rough opening. This will ensure the new door fits in your home. Follow these steps to get the dimensions of the rough opening: 

  • From the inside of your home, measure the width of the rough opening from stud to stud. Studs are the vertical 2x4s that support your home.


  • Measure at two to three different points along the width of the rough opening. Write down the smallest of those measurements.



  • Measure the height of the rough opening by looking at the bottom corners where the interior door casing used to be and locate the subfloor. The subfloor is the solid material that extends underneath your door unit and floor covering. 



  • Measure from the subfloor to the top of the rough opening on each side. Write down the smallest of these dimensions. Complete this step and you now have your rough opening width and height. 

3. Determine side jamb depth

The last step in measuring your exterior door involves obtaining 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 exterior edge of the side jamb to the interior edge, making sure not to include the exterior trim, such as brickmold or casing. 
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 door jamb depth, you have the measurements you need to determine which door unit will fit your home. 

Door swing: what you need to know

Door swing is an important element of any front door replacement project so you can plan for proper functionality and position your hardware correctly.  
Especially with front doors, think about how your current door swings so you can mirror that movement in your project. If your exterior door swings inside of your home when you open it from the outside, you have an inswing door. Conversely, if you have the pull the door open to enter, you have an outswing door.  

You may see door swing and handling mentioned together, but they are two different things. Not only do you want to know if your front door is an inswing or outswing, but it’s important to note if you have a left hand swing or a right hand swing. 
To do so, face your door outside and open it. If your door handle is on the right and you open your door from right to left, you have a left hand swing door. If your door handle is on the left and you open your door from left to right, you have a right hand swing door. 

Front door replacement options

When it comes to replacing your front door, Masonite offers a wide range of choices to enhance the beauty and functionality of your home’s entryway. Choose from an array of styles, designs and materials to suit different architectural preferences and personal tastes. 
Whether you’re seeking a classic look, a modern touch, or something in between, we offer options like fiberglass doors that mimic the look of real wood, steel doors that match any style and budget and various glass insert designs to allow natural light into your home. 

Last Updated: June 28, 2023