How to Measure Your Own Windows for Blinds or Shades

Greenwood Window Treatments · 2026-09-29

A tape measure and twenty minutes will get most homeowners a workable set of window numbers. Whether those numbers are accurate enough to order custom product on is a separate question, and it's worth answering honestly before you start writing figures down.

Deciding Inside or Outside Mount Before You Measure

If you're measuring a whole house in one sitting, walk every room first and make the mount call before you touch a tape anywhere. It's a lot faster to sort all your windows into inside mount and outside mount piles up front than to bounce back and forth between decisions room by room.

Inside mount needs a clear opening with real depth, usually at least 2 inches, and nothing like a crank or lock intruding into that space. Outside mount works around most of those limitations by mounting to the wall or trim instead of fitting inside the frame. A quick walk-through of a Greenwood house, checking depth and obstructions on each window, usually sorts most of them in under fifteen minutes.

Write the mount decision down next to each window as you go. You'll need it again in a few minutes once the actual measuring starts, and re-deciding it twice wastes time you don't need to spend.

Recording the Numbers Without Wrecking the Order

Rounding to the nearest inch instead of the nearest eighth is a quiet way to sabotage an otherwise careful measurement. It feels close enough. It isn't, and that gap is enough to leave a visible light gap on one side or keep a shade from clearing the frame on the other.

Writing height where width goes, or the other way around, is the other classic failure, especially late in a long measuring session when fatigue sets in and every window starts to blur together. Always write width first, then height, and label both clearly rather than trusting that you'll remember the order by the time you sit down to fill out the actual form.

If you're doing more than two or three Greenwood windows in one sitting, build in a system before you start: room name, smallest width, smallest height, mount type, written down together for each window before moving to the next one. Skipping that system is how a homeowner ends up with eight sets of numbers and no idea which belongs to which room.

The Tools That Actually Matter

A professional's kit for this job is shorter than people expect. A metal tape measure, not cloth, since cloth stretches with age and use in a way that throws off a custom order. A pencil and a notepad, since a phone's notes app is an easy place to fat-finger a number under pressure. That's most of it.

A stepladder earns its spot too, mainly because guessing a measurement from an angle below a tall window introduces error nobody needs. And a second person is worth recruiting for anything wider than a standard window, since holding a tape steady at one end while reading a number at the other is genuinely hard to do alone without the tape sagging.

• Steel tape measure
• Pencil and paper, not a phone app, for recording each figure
• A stepladder for anything above easy reach
• A second person for wide or tall windows

Skip a laser measure unless you've confirmed it reads exact fractions rather than rounding to the nearest quarter or half inch. That rounding is precisely the kind of small error that turns into a real fit problem on a custom order.

The Three-Point Measure, and Why One Number Isn't Enough

This is the step to be honest with yourself about before committing to DIY. It takes real patience: width at the top, middle, and bottom, height at left, middle, and right, six numbers written down per window rather than one quick reading in the center.

If that sounds like something you'll actually do carefully on every window in the house, DIY measuring is a reasonable option. If it sounds like the kind of step that gets shortened to close enough by window six of ten, that's useful self-knowledge, and it points toward getting a professional measure instead, at least for the windows that matter most.

There's no shame either direction. Some people genuinely enjoy this kind of careful, repetitive task. Others find it tedious enough that corners start getting cut without noticing, and a shortened three-point measure on a Greenwood window that turns out to be out of square is exactly how a custom order goes wrong.

What Happens When the Measurement Is Wrong

This is the part worth being straight about. Custom window coverings are built to the exact number you provide, and once they're cut and assembled, they generally can't be returned the way a stock item can. If the number's off by enough to matter, you're looking at paying for a remake rather than getting a refund, since the mistake was in the measurement, not the product.

That doesn't mean measuring your own windows is a bad idea. Plenty of Greenwood homeowners do it successfully every year, especially on straightforward rectangular windows with clear access and no obstructions. Where it gets risky is on anything unusual: a window with visible slope, one where you're not sure if there's clearance for inside mount, or a room with enough windows that one bad measurement is easy to lose track of among the rest.

If you've gone through the process and you're confident in the numbers, that confidence is usually earned and worth trusting. If something about a specific window feels uncertain, that's exactly the situation a second set of eyes is good for, and it costs nothing to have someone check before an order that can't be undone goes in.

Whatever you decide, get the number right before you order, because a custom shade or shutter doesn't come back once it's cut to a size. A free in-home measure is the simplest way to remove that risk, and it doesn't cost anything to book one.

Frequently Asked Questions

Why do installers measure width in three places instead of one?

Because almost no window is perfectly square, even in a newer house. Measuring at the top, middle, and bottom catches a frame that's narrower at one end than the other, and the order gets built to the smallest of the three so it actually fits.

Can I use a laser measure instead of a tape?

Some can work, but a lot of consumer laser measures round to the nearest quarter or half inch, which isn't precise enough for a custom order. If you use one, check that it reads out in exact fractions before you trust the number.

What's the single most common mistake in a DIY measurement?

Measuring only once, in the middle, and assuming the rest of the window matches. It usually doesn't, and that single number gets used to order a product built to a size that doesn't match the narrowest point of the actual opening.