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How to measure exterior doors?

Person measuring door using tape measure

Start by measuring the door’s width from one side to the other. For height, measure from bottom to top. Always round measurements to the nearest inch for accuracy. Read below for the full guide.

Why Accurate Measurements Matter

Accurate measurements aren’t just numbers on a tape measure; they’re the foundation of a successful home improvement project. But why, you might ask, is getting the exact dimensions of your exterior door so crucial? Let’s dive into the key reasons.

Safety and Security

Robber trying to break a door

Doors serve as the entry and exit points of your home, and a door that doesn’t fit its frame well could be easier to force open. A door that’s too small for its frame might not latch or lock properly, jeopardizing the security of your household.

Moreover, a poorly measured door can be a cause of unwanted accidents. Imagine a door that gets stuck or jams regularly; this can result in accidental injuries, especially if someone is in a rush and uses excessive force to open or close it. Children and the elderly are particularly at risk in such scenarios.


Visual appeal matters, and a door that doesn’t fit well simply looks odd. For instance, gaps between the door and its frame can not only be unsightly but also interfere with the overall architectural harmony of your home.

They might even leave you open to the elements, letting in rain, snow, or drafts that can damage your flooring or rugs over time.

Energy Efficiency

Doors serve as a barrier between the internal and external environments, affecting not just security but also your home’s energy consumption. A door that doesn’t properly fit its frame can let in drafts, driving up your heating and cooling bills. Over time, this can significantly impact your wallet.

Safety Precautions Before Measuring

Group of people wearing safety gear

When it comes to measuring and installing exterior doors, safety should never be an afterthought. Start by familiarizing yourself with the tool manuals and giving your tools a quick inspection before diving into the work.

If ladders are involved, always place them on a stable surface and keep your hands free while climbing. Personal protective gear such as gloves and safety goggles are a must to avoid any unnecessary injuries.

Keep your work area clean and well-lit to minimize the chances of accidents.

Measuring the Door Size

2 closed white doors and 1 open red door

Accurate measurements form the foundation for a seamless door replacement or installation experience. Below are some guidelines for different types of doors.

Single Doors

Beautiful red single door

For a standard single door, begin by measuring the width from one side of the door slab to the other. For the height, measure from the bottom of the door to the top. Always round up your measurements to the nearest full inch.

If your door is 37 3/4 inches in width and 81 1/2 inches in height, for example, your replacement should be a 38×82-inch door. Remember, these measurements are for the door slab itself, excluding frames or thresholds.

Double Doors

Elegant double door

Measuring double doors requires a bit more attention. Start by measuring the width of each door panel, and then sum them up for the total width.

For the height, the process is similar to a single door: measure from the bottom to the top of one panel. Again, round up to the nearest full inch. Make sure to note down both individual panels and total measurements.

Door With Sidelights

Black exterior door with sidelights

If your door setup includes sidelights, you’ll have a few additional measurements to take. Measure the width and height of each sidelight separately, rounding up as needed.

Combine these sidelight measurements with those of your main door (or doors, in the case of double doors) to determine the total width and height of the entire assembly, which will be essential when selecting or customizing a new door unit.

Measuring the Jamb Width

The jamb width is another key measurement you can’t afford to overlook. Getting this wrong could mean your new door won’t fit flush with your wall or may require extra work like adding jamb extensions.

What is Jamb Width?

Open door with bright light on the other side

Jamb width refers to the thickness of the wall frame where your door will be installed. Specifically, it is the measurement taken from the backside of the interior trim to the backside of the exterior trim.

Determining the Jamb Width

To measure the jamb width of your door, you’ll first need to identify the backside of both the interior and exterior trims that frame the door. Once you’ve pinpointed these areas, take out a tape measure and extend it across these two points to capture the distance between them.

It’s crucial to keep the tape measure level and in direct contact with the surfaces you’re measuring. For a more accurate measurement, it’s advisable to measure multiple areas of the jamb—namely, the top, middle, and bottom—and then compute the average.

Any variations in these readings could suggest an issue like warping or an unevenly installed jamb.

The Rough Opening

Teal exterior door

The term “rough opening” refers to the framed opening where your exterior door will be installed. It is essentially the hole in the wall that will accommodate your door unit, complete with its frame and any sidelights or transoms you may choose.

Measuring the Rough Opening

To accurately measure the rough opening for your new exterior door, begin by removing the interior trim surrounding your existing door. Next, use a tape measure to determine the width by measuring the distance between the framing members on either side of the opening.

For the height, measure from the bottom of the sill to the top of the framed opening.

Once you have these measurements, compare them to the rough opening requirements specified for your new door. This comparison is crucial as it will confirm that the door you plan to purchase will fit perfectly into the existing opening.

What if Measurements Don’t Match Standard Door Sizes?

When it comes to measuring exterior doors, precision is key. The right fit ensures energy efficiency, security, and a proper seal against the elements. But what happens if your measurements don’t align with the standard door sizes? Fear not, here’s a guide to help:

Consider a Custom Door

Contractor installing a custom door

If standard door sizes don’t align with your measurements, a custom door might be the solution. If you’re interested in having a custom door, we offer an interactive online tool where you can design and build your own door. Additionally, you can configure it to suit your preferences and receive an instant quote. While this might be a costlier option, it ensures a perfect fit tailored to your exact needs.

Modify the Door Frame

In some instances, it may be feasible to adjust or modify the existing door frame. This is a job best left to professionals, as it requires knowledge of structural integrity and might also involve some masonry or woodworking skills. To ensure the work is done correctly, consider getting a free quote from a qualified expert.

Adjustment with Door Accessories

Sometimes, minor discrepancies in measurements can be rectified with the use of door accessories. For example, weatherstripping can seal minor gaps, and threshold adjustments can address height discrepancies.

Understand the Importance of Clearance

Doors require a certain amount of clearance to open and close smoothly. If measurements seem tight, consider this clearance. You might need a slightly smaller door to account for the swing and prevent scraping.

Consider Door Expansion and Contraction

Wooden exterior single door

Materials, especially wood, can expand or contract based on the weather. Make sure you measure your door during a moderate climate to ensure a more consistent reading.


Getting the right measurements for your home projects, especially doors, is super important. A door is more than just a way in or out; it keeps your home safe, makes it look good, and helps control your home’s temperature. When a door fits just right, your home is more comfortable and secure.

And if your door measurements are a bit off from the usual sizes, don’t worry. There are many ways to make it work, like getting a custom door, fixing up the frame, or using extra door items. Whatever you choose, remember that the goal is a door that works well and looks great.

Fact checked by Jacob Petrosky – 9/15/23