According to the International Association of Certified Home Inspectors, aluminum windows should last 15 to 20 years and wooden windows for at least 30. That means you may need to replace your windows at some point.

Window replacement may seem like a simple task, but it’s easy to make mistakes that could lead to delays and headaches. We’ve spent hundreds of hours researching the best replacement windows to break down how to measure your windows. In this guide, we’ll also provide our top recommendations for professional window installers once your measurements are completed.

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Windows Glossary

Before you get started, there are some terms you need to know to measure windows correctly.

• Balance: These are spring-loaded, mechanical devices commonly found in single- and double-hung windows. They help to counterbalance the weight of the sash during opening and closing.
• Frame: The window frame surrounds and supports the entire window system. A window frame consists of the head, jamb, and sill.
• Head: The window head refers to the central horizontal part that forms the top of the window frame.
• Jambliner: This is the strip on each side of a window that helps fit the window sash.
• Jambs: These are the main vertical parts that form the sides of the window frame.
• Lift: The lift refers to the handle for raising the lower sash.
• Rails: For double-hung windows, there are three rails. The upper and lower rails create the horizontal piece of the window sash. The middle rail, or the check rail, is where the bottom part of the upper sash meets the upper part of the lower sash.
• Sash: This is the movable part of a window that holds the glass.
• Sill: This term refers to the central horizontal part that forms the bottom of the window frame.

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How To Measure Windows

Once you have your tape measure ready, use these three primary steps to accurately measure existing windows:

1. Width: First, measure the window’s width. To do so, measure between the jambs at the window opening’s top, middle, and bottom. Measure from the surface of the jambs and not from the trim strips or parting beads. When you order a new window, use the smallest of these three width measurements for the dimensions.
2. Height: Next, measure the window’s height. Measure from the high point of the window sill at the surface closest to the inside of the window to the top of the window opening. Take this measurement from the left side, center, and right side of the window. Again, use the smallest of these three height measurements when you order the new window.
3. Depth: Finally, measure the depth of the window opening. There must be at least 3 1/4 inches of opening depth between the inside window trim and the outside blind stop strip. This much area is necessary to accept the depth of the replacement window. If your window features any pulleys or parting strips, ignore them when measuring depth dimensions since the installer will remove them.

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Find a Local Window Installer

Once you have the measurements and know what type of window you want, it’s time to figure out window replacement installation. While you can install windows yourself, it’s easy to do incorrectly if you don’t hire a local window installer. There are many window installation companies, so one way to whittle down your options is to look for certified installers for the window brand you want. You should also confirm which companies service your address.

Our tool below can quickly connect you with reputable, certified window installers that service your ZIP code and schedule in-home assessments.

Otherwise, these are some of our top recommendations for professional window replacement. 

Champion Windows: Best Financing

• Our rating: 85.5 out of 100
• Warranty: Limited lifetime warranty
• Price range: $350–$800

Champion Windows was founded in 1953 and now provides window lines in 28 states. The company’s ColorBond aluminum window line uses nontoxic heat-reflective materials to maintain cool temperatures in your home. The TimberBond line offers custom wood grain finishes such as cherrywood, dark oak, and English oak.

In addition, Champion Windows provides sunroom and patio services. The company builds all-season and three-season sunrooms with custom-shaped windows tailored to your home’s style.

Castle Windows: Best Warranty

• Our rating: 90 out of 100
• Warranty: Transferable lifetime warranty
• Price range: $300–$600

Castle Windows has offered high-quality replacement windows, doors, roofing, and siding services since 1977. The company provides accessible windows with double weatherstripping for durability. Castle creates made-to-order windows rather than offering specific lines. It has wood, fiberglass, and aluminum window options. 

The company includes a transferable lifetime warranty covering all window parts, including glass and screens. Castle’s warranty also covers workmanship with free labor on all services—a standout compared to standard manufacturer warranties.

Renewal by Andersen: Most Hands-Free Install

• Our rating: 94 out of 100
• Warranty: Limited and limited lifetime warranties
• Price range: $500–$3,000

Andersen is one of the most recognizable names in the windows industry. Its subsidiary, Renewal by Andersen, offers customized replacement windows with white-glove service. In addition, you can schedule a free consultation with a window specialist to determine your window needs and specifications.

Renewal has 35 different window styles, including specialty shapes. In addition, you can select from various exterior colors, interior colors, glass types, hardware colors, grille patterns, and an optional TruScene insect screen. Those who want standard Andersen windows can find the brand at popular retailers such as The Home Depot.

Andersen backs its products with a limited or limited lifetime warranty, depending on the item.

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Our Conclusion

Before replacing them, make sure you know how to measure windows. This guide will help to ensure that you take measurements in the right spots. While a few windows could be a do-it-yourself (DIY) job, a professional window installer will make sure that everything goes well.

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FAQ About How To Measure Windows

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Our Rating Methodology

We back up our window ratings and recommendations with a detailed rating methodology to objectively score each provider. We conduct research by speaking with company representatives, browsing product selections, analyzing window line specifications, and conducting focus groups and consumer surveys. We then score each provider against our review standards for window variety, value, trustworthiness and transparency, window features, and customer service to arrive at a final score on a 5-point rating scale.

To share feedback or ask a question about this article, send a note to our Reviews Team at reviews@thisoldhousereviews.com.