How to Measure Your Windows for Replacement: The Complete Denver Homeowner’s Guide

Getting a window measurement wrong by even a quarter inch can mean weeks of delay while a manufacturer rebuilds your order. If you’re planning a replacement project, you need three numbers: width, height, and depth, each measured in three places. Here’s exactly how to get them right the first time.

Denver homes have a habit of throwing off first-time measurers. Houses built in the 1950s and 60s through Harvey Park, Park Hill, and older stretches of Aurora often have window openings that have shifted slightly over 60-plus years of settling. Newer builds in Highlands Ranch or Parker tend to be more standardized, but “standard” still varies by builder. Either way, the tape measure doesn’t care what the blueprints said. It only cares what’s actually there today.

What You Need Before You Start Measuring

A steel tape measure, a pencil, and a notepad will get the job done. Skip the cloth or fabric tape measures. They stretch slightly over time and that small amount of give is exactly the kind of error that leads to an ill-fitting window.

Measure in inches to the nearest eighth. If you’re ordering from a company that also works in millimeters, note both, but inches are the standard for most U.S. residential window manufacturers.

Work from inside the house. Interior measurements give you the true opening size, which is what matters for ordering a replacement window that fits the existing frame.

How to Measure Window Width

Measure the width at three points: the top of the opening, the middle, and the bottom. Measure jamb to jamb, meaning from the inside edge of one side frame to the inside edge of the other.

Write down all three numbers. Older window openings are rarely perfectly square, and the difference between the top and bottom measurement can be a quarter inch or more. Use the smallest of the three numbers as your width. Ordering to the smallest measurement means the new window will fit even in the tightest part of the opening.

How to Measure Window Height

Do the same thing vertically. Measure from the top of the opening down to the sill at three points: the left side, the center, and the right side.

Again, record all three and use the smallest measurement. A window opening that’s 36 inches tall on the left and 35 and three-quarters on the right needs to be ordered at 35 and three-quarters. It’s a small difference, but it’s the difference between a window that slides into place cleanly and one that needs to be forced or shimmed excessively.

How to Measure Window Depth

Depth is the one homeowners forget most often. Measure from the interior trim to the exterior trim, or if there’s no interior trim, from the front of the interior wall surface to the back of the exterior wall surface.

Depth matters because it determines what type of window unit you can install and how much room there is to work with for insulation and flashing around the new unit. A shallow depth might rule out certain frame styles or require a different installation approach altogether.

Should You Measure the Frame or the Glass?

Measure the frame opening, not the glass. The glass measurement tells you nothing useful for ordering purposes. What matters is the rough opening, the actual space the window has to fit into, measured jamb to jamb and sill to head. Any reputable window company will ask for opening measurements, not glass size.

Common Measuring Mistakes That Cost Denver Homeowners Money

The most common error is measuring only once, in one spot, and assuming the whole opening is that size. Skip that shortcut. Openings shift over time, especially in homes with a few decades on them, and one measurement won’t catch it.

The second common mistake is using a fabric tape measure instead of steel. That stretch adds up.

The third is measuring the visible glass instead of the actual opening. This one alone accounts for a large share of ordering mistakes we see from homeowners who try to order windows online without a professional measurement first.

Finally, some homeowners round up “to be safe.” Don’t. Rounding up is exactly how you end up with a window that doesn’t fit and has to be special-ordered a second time, adding weeks to your project.

Why Professional Measurements Still Matter, Even If You Do the Math Yourself

Knowing how to measure your windows is useful information whether you’re planning ahead, comparing quotes, or just curious what a replacement might cost. But when it comes time to actually order, a small measuring error can turn into a big problem. Manufacturers build windows to the measurement they’re given. If that measurement is off, the window either won’t fit or will fit poorly enough to affect the seal, the energy performance, and the long-term durability of the installation.

That’s why any legitimate window company will send someone out to confirm measurements before placing an order, no matter how confident you are in your own numbers.

Measuring your own windows is a good way to understand your project and set realistic expectations before you start collecting quotes. But once you’re ready to order, it pays to have a professional confirm every number. At JDI Windows, our team measures every opening in person as part of the quote process, so what gets ordered is exactly what fits your home. If you’re ready to see what a proper Denver window replacement looks like, we’re happy to come take a look.

Frequently Asked Questions