How to Measure Your Windows for Blinds — The Right Way (And the Mistakes That Cost People Money)
By The Blinds Authority
If you’ve ever ordered blinds online and ended up with something that didn’t fit, you’re
not alone. Measuring windows is the single most common question new buyers ask —
and it’s also where most costly mistakes happen before a single blind is ever installed.
After years of helping thousands of customers navigate this exact process, I can tell you
the problem isn’t that measuring is hard. It’s that most people don’t know two critical
things going in: whether to add or subtract inches, and how much depth their window
frame actually has. Get those two things right, and the rest is straightforward.
Here’s everything you need to know before you touch a measuring tape.
Step One: Decide Between Inside Mount and Outside Mount
Before you measure a single thing, you need to make this decision — because it changes
everything about how you measure.
Inside mount means the blind sits inside the window frame, creating a clean, built-in
look. Most people prefer this option because it looks more finished and intentional.
However, inside mount requires a minimum of 1.5 to 2 inches of depth inside your
window frame to physically mount the hardware. If your frame is shallower than that,
inside mount simply isn’t an option.
Here’s how to check: grab a tape measure and measure straight back into the window
frame from the front edge. If you have at least 1.5 inches — preferably 2 or more —
you’re good for inside mount. Some specialty products require even more depth, so
always check the specific product’s requirements before ordering.
Outside mount means the blind mounts on the wall above or on the face of the window
frame. This option works for any window regardless of depth, and it’s also useful when
you want to make a window appear larger than it is, or when you need to block morelight by extending the blind beyond the frame edges.
Bottom line: If you have the depth, most people choose inside mount for aesthetics. If
you don’t, outside mount is your answer — and it looks great too.
Step Two: Measure for Inside Mount
For inside mount, you’re measuring the interior of the window frame — the actual
opening.
Width: Measure the width of the window opening in three places — at the top, middle,
and bottom. Windows are rarely perfectly square, especially in older homes. Use the
narrowest measurement of the three. This ensures the blind will fit without jamming.
Height: Measure the height of the window opening in three places — left side, center,
and right side. Use the longest measurement of the three.
Do NOT add or subtract anything. This is one of the biggest points of confusion for
online shoppers. When you order an inside mount blind, the manufacturer automatically
deducts a small amount (typically 1/4 to 3/8 of an inch) from the width to ensure the
blind fits properly inside the frame. You order the exact size you measured — they
handle the deduction. Always confirm this in the product’s ordering instructions,
because it varies slightly by manufacturer and product type.
Record your measurements as: Width x Height (width always comes first in the window
covering world).
Step Three: Measure for Outside Mount
For outside mount, you have more flexibility — because you’re deciding how much of the
wall or frame to cover.
Width: Decide how far beyond the window frame you want the blind to extend on each
side. A minimum of 1.5 to 2 inches on each side is recommended for light control. Many
people go 3 inches or more on each side, especially in bedrooms where blocking every
bit of light matters. Add those extensions to the width of your window frame opening.
Height: Measure from where you want the top of the blind to sit (usually 2–4 inches
above the window frame) down to where you want it to end. For maximum light blocking,
extend the blind to the windowsill or slightly below it.
For outside mount, you order the exact size you want the finished blind to be. Nodeductions are made. What you order is what you get.
The Most Common Measuring Mistakes (And How to Avoid
Them)
These are the mistakes that result in returns, refits, and frustration — and they’re all
avoidable.
Mistake 1: Not following the measuring guide for that specific product. Every
manufacturer has a measuring guide, and the details matter. Some products have
different deduction policies. Some motorized blinds require additional clearance. Always
read the measuring instructions on the product page before you order, not after.
Mistake 2: Skipping samples. Before spending hundreds of dollars on blinds for your
entire home, order samples. Every major retailer offers them — often free or for a
nominal fee. Hold the sample against your window in different lighting conditions. What
looks perfect on a screen can look completely different in your actual space. This single
step prevents the majority of buyer’s remorse.
Mistake 3: Measuring once. Measure every dimension at least twice, preferably three
times. Write down each measurement as you go. Don’t rely on memory, and don’t round
up or down unless the instructions tell you to.
Mistake 4: Having unrealistic expectations about delivery time. Custom window
coverings are made to order. They are not in a warehouse waiting to ship. Production
times typically run 5–10 business days before shipping even begins, and that’s before
transit time. Plan accordingly, especially if you’re working toward a move-in date or an
event.
Mistake 5: Not considering professional measurement services. Most major
retailers offer a low-cost professional measure and install service. If measuring feels
overwhelming, or if you have difficult windows — arched, very large, or unusually
shaped — this service pays for itself in avoided mistakes. It’s one of the most underused
options available to online shoppers.
A Quick Room-by-Room Guide
Not all windows need the same thing, so before you measure, know what you’re
measuring for.Living rooms and common areas: Most people choose light filtering products here —
they soften natural light while maintaining a view and privacy during the day. 2-inch faux
wood blinds are the most popular choice and the best value at almost every price point.
Bedrooms: Blackout or room darkening products are the standard recommendation.
These block enough light to sleep comfortably regardless of the time of day. Cellular
shades with blackout liners are a popular option here because they also add insulation.
Nurseries and media rooms: Same recommendation as bedrooms — blackout is the
right call. Light control is the priority, and there’s no such thing as too dark in a nursery
or home theater.
Bathrooms: Moisture resistance matters here. Faux wood blinds are ideal because
unlike real wood, they don’t warp or crack in high-humidity environments. Light filtering
is typically sufficient for privacy at most window heights.
The One Question to Ask Yourself Before You Buy Anything
Before you measure, before you browse, before you compare prices — ask yourself one
question:
What do I actually need this window covering to do?
Privacy, light control, both, or neither. Start there, and every decision after that
becomes easier. The product category, the color, the price point — all of it flows
naturally from that single answer.
Most people skip this step and end up overwhelmed by options. Start with your need,
not the product.
Ready to Order?
Once you have your measurements, check out our buying guides for specific product
recommendations at every budget level. And if you have questions about a specific
window situation — unusual depths, awkward shapes, or rooms with specific needs —
browse our FAQ or drop a question in the comments below.
Getting this right the first time saves you money, time, and the frustration of a return.
Take the extra ten minutes to measure correctly. Your windows will thank you.The Shade Authority is an independent window covering resource built on years of
professional sales experience with the industry’s leading retailers. We earn a
commission when you purchase through our links, at no additional cost to you.