A comprehensive guide on how to measure windows for replacement

Table of contents

1. The preparatory work to be done before taking measurements of any windows
2. Step-by-step instruction to take measurements of the window
3. Additional tips on how to take measurements of the window if you're not a pro
4. Does it make sense to hire a pro to take window measurements?

Have you ever wondered why your electricity bills rise from year to year? Except for the non-stable energy market and seasonal spikes, the culprit might be the old, drafty windows. Around 30% of the air accumulated by your HVAC system is lost through the low-efficiency home windows. That means you pay for energy that wastes in vain. The telltale signs like leakage, drafts, fog between the panes, uncomfortable temperature inside, and skyrocketing electricity bills point to the windows losing their insulation properties. If that's your case, there is no room for doubts that your windows should be replaced without delay. 

Installing new energy-efficient windows is a great way to ensure better home insulation and weatherproofing. Plus, you will significantly reduce your annual spending on electricity and boost your home's resale value. Modern windows come with excellent energy-saving properties, which means the load on your heating and cooling system will be lower. At the same time, you'll enjoy a comfortable temperature all year round. 

However, like with any other home improvement project, everything should be done consistently from the very beginning. The starting point is to take measurements of the window frame. Once this step is done, you can pick the unit that fits. Whether you want to skimp on professional installation or hire local window pros, it's helpful to have your own set of measurements to control the process from A to Z. The tips given in this guide will help you get the correct measuring for replacement windows even if you lack expertise. Read on to make things right and avoid rookie mistakes.

The preparatory work to be done before taking measurements of any windows

Finding the window size is not a complicated task. Nevertheless, taking accurate measurements without the right tools and knowledge might be tricky. Take your time to get it right and ensure you're thoroughly prepared.

First off, check the condition of the existing frame. If it features water damage or rot signs, getting a replacement window is not your choice. Deteriorated frames are not structurally sound enough to support a replacement unit and should be dismantled. That means you should set your sights on installing a new window instead. However, if the existing frame looks good and has the right square construction, you can continue your preparations for replacement. 

Once you deal with the existing frame, gather the needed tools for taking window measurements. Take a tape measure, pencil, a piece of paper, or a worksheet. You can save a lot of time and effort working in pairs. For example, you will take measurements while another person writes them down.

Step-by-step instruction to take measurements of the window

Check windows for square

It's crucial to determine whether all four corners of the window frame have 90° angles. Don't omit this step, as installing a replacement unit in a lopsided frame will cause further window operation issues.

To check the window for square, you need: 

• All window measurements should be made from inside the home. 
• Measure a frame diagonally from the top right corner where the horizontal and vertical trim boards meet
• Measure a frame diagonally to the lower-left corner where the trim meets 
• Record the received measurement
• Take similar window measurements in the other diagonal direction
• Record the received measurement
• If the dimensions are within 1/4-inch of each other, you can opt for most standard window sizes, and they should fit the frame tightly.
• If the obtained measurements are not within 1/4-inch of a square, the options are to go for a new-construction window or square up the existing frame. 

Measure window width

Find the inside jamb and hold the tape measure taut from this point to the right and left sides of the window. The width should be measured at the top, middle, and bottom.

• To get the top measurement, you should measure the window from jamb to jamb at the highest point. The work should be undertaken while the window is closed. 
• To get the middle dimension, you need to measure the window from jamb to jamb close to the middle. These measurements should be taken while the window is fully opened. 
• To get the bottom measurement, you should measure the window from jamb to jamb at its lowest point. Slide the window up to take accurate measurements.
• Record the received dimensions and highlight the shortest one. This number is the window opening width. 

Measure window height

To get the window height dimensions, you have to measure it from the bottom sill to the top of the head jamb. The measurements should be done on the far left and far right sides from the sill to the header and in the center of the window unit. Record the achieved numbers and highlight the shortest one. This is the window opening height.

Many DIYers mess up with the sill position. Please note that measurements should be made not from the so-called window stool that extends into the room but from the horizontal board on which the window sash is based.

Measure window depth

To find out the window depth, measure the sill space from the back to the front of the trim. Make sure to open the window before taking these measurements. The space between the front and the back of the trim should be a minimum of 3¼ inches. This dimension gives you the green light to go for a standard-sized replacement window.

If the depth is too narrow to mount a replacement unit, it's better to get a professional consultation. In most cases, homeowners are advised to give up the idea of replacement and install a new construction window instead. This problem is common for modular and mobile homes and rarely happens in traditional residential buildings.

Round down the numbers

When you know the window's square, width, height, and depth, take the highlighted measurements and round them down to the nearest ⅛ of an inch. If the received size is already in an ⅛ increment, keep it as it is. The final dimensions are meant for ordering the new replacement windows.

Additional tips on how to take measurements of the window if you're not a pro

If you decide to handle the window replacement project yourself, make sure to approach the steps in the correct sequence. Start with examining the existing frame condition, check window square, width, height, and depth, and record your findings. It won't hurt to double-check the received window measurements if you take them for the first time, as accuracy is critical. 

Once you are done with it, choose and purchase the replacement window. It's highly recommended to buy custom replacement units based on the exact numbers. The brick-and-mortar home improvement stores often have a poor assortment, and the risk is you may get a unit close in dimension but not precise.

Does it make sense to hire a pro to take window measurements?

A few factors may affect your decision on whether to hire an expert window installer or do everything from measuring to installation on your own. First off, consider the number of windows you're about to replace. It can be very time-consuming if you want to cover the entire house and change 4-5 windows. In this case, we recommend relying on the installers' crew. Plus, if you have non-standard windows in form or size, your DIY attempts might fail as the process of their replacement is rather complicated and requires a bunch of experience. 

However, if you still want to replace the home windows yourself but have doubts regarding the accuracy of the measurements, call out a local window contractor to recheck them. Depending on the region, it will cost you from $60 to $95 per hour. However, this price is much lower than the carpenter's rate for dismantling the wrong-sized window unit.

If you need a window professional ASAP and lack time looking through the local installers' offers, the MyHomeQuote contractor-matching platform is the answer. We boast a considerable pull of certified specialists in every state, so it will take us less than an hour to match you with the right pro. All it takes is to leave your request on our platform.