How to Measure Windows and Doors: A Homeowner's Guide

Measuring your windows and doors is a useful first step when planning a replacement project. Whether you're checking sizes for an initial estimate or getting ready for a professional measurement appointment, having a general idea of your window and door dimensions can make the process easier.

You don't need specialized equipment to get started. A measuring tape works well for most openings, and modern smartphones can even estimate dimensions using augmented reality (AR) technology.

In this guide, we'll explain how to measure your windows and doors using both methods, what measurements actually matter, and how to prepare your home before a Northline measurement appointment.

Measuring Windows and Doors Using Your Smartphone

Many modern smartphones support augmented reality (AR), a technology that uses your phone's camera and sensors to estimate the dimensions of objects around you.

This can be particularly useful when measuring large windows, patio doors or openings that are difficult to reach with a traditional measuring tape.

How to Take Measurements Using AR

On a compatible iPhone, you can use Apple's built-in Measure app. Android users can explore compatible AR measurement apps, such as iScanner.

Here's how to get started:

1. Open your measurement app. On an iPhone, locate the Measure app. If you're using Android, open an AR measurement app that supports your device.

2. Point your camera at the opening. Stand far enough away that the entire window or door frame is visible.

3. Mark the starting point. Position the on-screen measurement guide at one edge of the opening.

4. Measure the width. Move the guide horizontally to the opposite edge and record the measurement.

5. Measure the height. Repeat the process vertically, from the bottom of the opening to the top.

6. Save your measurements. Take a screenshot or write down the dimensions, noting which window or door they belong to.

For better results, make sure the opening is well-lit and the edges of the frame are clearly visible.

Are smartphone measurements accurate enough?

AR measurements are helpful for getting a general idea of window and door sizes, especially when planning a project or discussing an initial estimate.

However, smartphone measurements are approximate. They should not be used as the final dimensions for manufacturing or ordering replacement windows and doors.

How to Measure a Window With a Tape Measure

A traditional measuring tape is still one of the simplest ways to measure a window opening. For preliminary measurements, you'll only need a tape measure, something to record your results, and a few minutes per window.

Before starting, it's helpful to understand the difference between the window itself and the surrounding opening.

The window frame is the structure that holds the glass and operating parts in place. The surrounding trim is decorative material that covers the transition between the window and the wall.

For an initial measurement, you'll generally want to measure the opening inside the existing frame rather than including the decorative trim.

Step 1: Measure the Window Width

Place your tape measure horizontally between the inside edges of the window frame.

Take three separate measurements:

• Across the top of the opening.

• Across the middle of the opening.

• Across the bottom of the opening.

Write down all three measurements and identify the smallest one.

You might notice that the measurements differ slightly. This can happen when an existing frame is not perfectly square, particularly in older homes where settling or previous installation work may have affected the opening.

Step 2: Measure the Window Height

Next, measure vertically between the upper inside frame and the window sill.

Again, take three measurements:

• Along the left side.

• Through the centre.

• Along the right side.

Record each measurement and identify the smallest one.

Be sure you're measuring to the actual window sill rather than the decorative ledge that may extend into the room.

Step 3: Record Your Measurements

Write down the width and height of each window, along with the room where it's located.

For example:

Living Room Window

• Width: 48 inches

• Height: 60 inches

• Location: Living room, front wall

Always record window dimensions as width × height.

Even if two windows appear identical, measure them separately. Small differences between openings are common.

These measurements are useful for preliminary planning. The exact reference points and final dimensions will depend on whether the installation involves replacing the existing window within its frame or removing the entire frame.

How to Measure a Door Opening

Measuring an exterior door is similar to measuring a window, but there's an important distinction between the door slab and the complete door assembly.

The door slab is the part that swings open and closed. The complete door assembly includes the slab, surrounding frame, threshold and other components.

If you're planning to replace an entire exterior door, measuring only the slab won't tell you everything about the size of the existing opening.

Step 1: Measure the Door Width

With the door safely open, measure horizontally between the inside edges of the door frame.

Take measurements near the top, middle and bottom of the opening.

Record all three measurements, paying attention to any differences.

If you're only able to measure the door slab, make a note of that rather than treating it as the full opening width.

Step 2: Measure the Door Height

Measure vertically from the upper inside frame down to the threshold, which is the bottom part of the doorway that you step over.

Check the height at the left and right sides of the opening, and record any differences.

Avoid removing trim or other parts of the doorway to expose the framing. A professional can assess those details during the measurement appointment.

Step 3: Note the Door Configuration

Exterior doors come in several configurations, and the overall dimensions can vary considerably.

Along with your measurements, make a note of whether your entrance has:

• A single entry door.

• Double entry doors.

• One or two sidelites (narrow glass panels beside the door).

• A transom window above the door.

• A sliding patio door or garden door.

These details help identify what you're looking to replace and what additional measurements may be required.

How to Prepare for Your Professional Window and Door Measurement Appointment

If you've scheduled a measurement appointment with Northline Windows & Doors, there's no need to measure every opening yourself beforehand.

Our team will take the measurements needed for your replacement project and assess the existing openings. However, a little preparation can make the appointment easier and help ensure every window or door is accessible.

1. Clear the Areas Around Your Windows

Move furniture, plants and other household items away from the windows being measured.

You don't need to empty the room. The goal is simply to provide enough space for the person taking measurements to approach the window and inspect the surrounding frame.

If a window is located behind a large piece of furniture that cannot easily be moved, let us know ahead of time.

2. Make Curtains and Blinds Accessible

Curtains, blinds and other window coverings can sometimes obstruct access to the frame.

Where possible, open your curtains and raise your blinds before the appointment.

There's usually no need to remove installed window coverings unless you've been specifically asked to do so.

3. Ensure Doors Can Be Opened

For exterior door measurements, make sure the doors being replaced can be opened and accessed safely.

Clear any shoes, storage items or furniture that might obstruct the doorway.

If a door is difficult to open, sticks against the frame or has a damaged lock, mention this during the appointment. These details can help explain problems with the existing opening.

4. Provide Access to Every Area Being Measured

If you're replacing windows in several rooms, make sure each room is accessible.

This may include bedrooms, basements, utility rooms or other spaces that are not used regularly.

For openings that can only be accessed from the exterior, ensure gates and walkways are accessible where practical. You don't need to climb ladders or attempt to reach difficult openings yourself.

5. Make Note of Any Existing Problems

A measurement appointment is also a useful opportunity to point out issues you've noticed with your current windows or doors.

For example:

• Drafts or cold air around the frame.

• Condensation between the glass panes.

• Windows that are difficult to open or close.

• Water stains or visible damage near the opening.

• Doors that stick, sag or don't close properly.

These issues may affect the type of replacement or installation method recommended for your home.

Why Professional Measurements Still Matter

Taking your own measurements is helpful for understanding the approximate size of your windows and doors, but replacement projects require more than a simple width and height.

A professional measurement appointment also considers the condition of the existing frames, the depth of the opening, whether everything is level and square, and the installation method being used.

For example, a window being installed inside an existing frame may require different measurements than one being replaced along with its entire frame.

The same applies to exterior doors, where the threshold, surrounding framing and door configuration can affect the replacement.

That's why homeowners should avoid ordering custom windows or doors based solely on their own measurements.

Getting Ready for Your Northline Measurement Appointment

If you have an upcoming measurement appointment with Northline Windows & Doors, the most helpful thing you can do is make sure the areas around your windows and doors are accessible.

You don't need to remove existing frames, take apart any trim or calculate the exact dimensions yourself.

Our team will handle the measurements needed for your replacement project, while giving you an opportunity to ask questions about your existing windows, doors and installation options.

A little preparation beforehand helps make the visit straightforward and ensures we can properly assess the openings being replaced.