How to Measure for a New Door - Renewal by Andersen®

A simple way to spruce up your home is by replacing your front door. Perfect for a quick home improvement project or adding an extra decorative touch, a replacement door is just the thing to welcome you and your visitors into your home. Since the front door is the first thing you see, you want it to be beautiful, inviting and in top condition.

If it’s time to replace your front door, our guide will help you learn how to measure a door for replacement.

6-Step Exterior Door Measurement Guide

Before shopping for your replacement exterior door, you need to have the right measurements. That starts with gathering the right tools. Get a tape measure, a pencil and a notepad to write down each length. You also need to determine if you’ll be replacing just the door or the entire prehung door unit, including the door frame, hinges, slab and trim. Installing a new door slab is generally an easy DIY project, but replacing the entire unit may require expert assistance.

Keep in mind that doors come in different shapes and sizes, and it’s OK if your measurements differ from the standard. The standard measurements in the U.S. are:

Width: 30 to 45 inches
Height: 71 to 96 inches
Thickness: Around 2 inches

Now, we can move on to measuring!

Step 1: Measure the Door Slab

Start by measuring the door slab. This part of the door is the panel that opens and closes, secured with a lock mechanism. Essentially, it’s the door without the frame.

Measure all aspects of the door slab, which includes:

Height: From the bottom of the door slab, hook your tape measure and run it up toward the top, just before the door frame. Repeat this measurement at different points of your door for an accurate reading.
Width: Secure and pull the tape measure horizontally across the door slab from one side to the other. This measures the distance between the left and right edges of the door slab.
Thickness: Open the door to expose the side edge. Place your tape measure on the outer face of the door and measure across the side edge to the inner face.

Ensure the tape measure is straight and taut for a precise reading. Measurements may differ if your door or frame isn’t level or straight. If you’re only replacing the door slab, you can stop your measurements here. If you’re installing a replacement prehung unit, you’ll need additional dimensions to ensure a perfect fit.

Step 2: Measure the Door Frame

The door frame is the framework installed into the wall opening to support the door, allowing it to hang, swing and close easily.

Same as the slab, you need to measure:

Height: Measure from the floor to the top of the frame. Note the measurement at various points along the door’s height to see if the frame size changes.
Width: Measure the frame width horizontally at three points, including both edges of the door frame.

For the most accurate reading, make sure your tape measure is straight and level.

Step 3: Measure the Door Jambs

This step is often overlooked when measuring for an exterior door replacement. However, the dimensions for door jambs are just as important for ensuring your door fits flush with the frame and keeps drafts and weather out.

Door jambs are the inner vertical panels of a door frame where your door is secured with hinges and a lock mechanism. There’s the hinge jamb, where the door’s hinges are mounted, and the strike jamb, where you’ll see the strike plate. This is also measured as door frame thickness.

Here’s how you measure these parts of the door:

Measure the door frame without the wall trim or casing. From one edge of the door frame to the other, place your tape measure horizontally and measure across the width of the door jamb panels.
Measure the casing, which is the space between the wall and the door frame. This will tell you the trim size you need to place around your door.

Step 4: Measure the Door Frame Opening

You’ll also need to measure the door frame opening. This opening is the hole in the wall where your door frame is installed and secured, meeting the house’s brickwork.

Here’s how:

Your tape measure must be placed against the edge of the brick or wall opening. This is just above the trim.
Measure the height of the door frame opening by running the tape measure from the top brick head down to the threshold or sill. Do multiple measurements at different points of the opening.
Measure the width brick-to-brick horizontally from one edge of the opening to the other.
Record the thickness of the door frame opening or the wall.

Step 5: Measure the Sidelights

Don’t forget to include sidelight dimensions if they’re part of your prehung unit. Sidelights are the narrow vertical windows on either side of the door, used for aesthetics and bringing more light into your entryway.

Keep these measurements separate:

Start by measuring the width and height of the door itself. You already have these dimensions from the steps above. Copy them onto a separate section of your paper for the sidelights.
Measure the width and height of each sidelight separately. Usually, they’re both the same size, but it’s best practice to measure each for accuracy.
Calculate the total width by adding the door and sidelight measurements together.

Sometimes, a home has one sidelight alongside its entry door, while others have none. You can adjust this calculation to suit your door and its components.

Step 6: Determine the Door Swing

Take a moment to check whether your door is inswing or outswing. Not all door swings the same way, but if you are looking to change their direction and orientation, this needs to be noted as it affects the position of the door’s hinges and lock mechanism. To identify which way your door swings, watch its direction of travel. If you push it to enter your home, it’s an inswing door. If you need to pull the door, it’s an outswing door.

Also, consider whether it’s a right- or left-handed door by locating the hinges. If they’re on the right, it’s a right-handed door. And if they’re on the left, it’s left-handed.

Tips for More Accurate Door Measures

These tips will help you take more accurate measurements:

Use the three-point measurement technique: Record at least three points for each measurement to check for unevenness in the door or its components. Take dimensions from the top, middle and bottom, as well as both sides.
Check for squareness: Measure the door diagonally from the top to the bottom corner. If both sets of measurements match, the door is perfectly rectangular. You can do the same for the door frame and opening.
Double-check your measurements: Take multiple measurements, as incorrect readings can lead to costly mistakes.
Use a laser measure: For easier measuring, consider replacing your tape measure with a laser one. They’re ideal for wider measurements, especially across double doors.

Now that you have everything you need, you can shop for a door that matches your home and style.

Let Renewal by Andersen® Fit Your Replacement Door

Fitting a replacement door is more than enhancing your home’s curb appeal. It’s also about improving energy efficiency and security, and ensuring your door is wear and tear-free. And if it’s time for you to replace your old faithful, we’re here to help you.

Renewal by Andersen® offers the nation’s best window and door replacement solution, with over 30 years of experience to meet all your replacement needs. You can find us throughout North and South Carolina, in Charlotte, Greenville, Asheville, Spartanburg, Columbia, Charleston and Hilton Head.

Need help with choosing the right size, color and shape to fit your style or want more information about how to measure for your new door? Contact us today for a free consultation with expert designers to bring your aesthetic vision to life.