I need to buy new blinds but I’m not sure how to properly measure my windows. I tried using a tape measure but I’m confused about whether I should measure the inside or outside edges. Any advice or step-by-step guide would really help.
Grab your tape measure, a pencil, and a piece of paper because it’s time to pretend we’re grown-ups for 10 glorious minutes. First, figure out if you want inside-mount or outside-mount blinds. Inside mount means the blinds sit within the window frame. Outside mount means they hang over the frame, covering a bit more wall (probably hiding all the weird paint mistakes from your last DIY attempt).
For inside mount (most people do this):
- Measure the width. Measure across the top, middle, and bottom INSIDE the window frame. Write all three down. The smallest number wins—use that to make sure your blinds won’t jam like a printer on Monday morning.
- Measure height: Measure from the top inside edge to the bottom (again, left, middle, right). Tallest number wins here, so the blinds will reach the sill and you won’t look like you bought capri pants for your window.
- Depth: Real quick, check from the glass to the edge of the trim to make sure the blinds will even fit inside. Most stores tell you how much you need based on the style you want.
For outside mount:
- Width: Measure the total width you want the blind to cover (usually add 2–3 inches on each side past the window frame).
- Height: Go from where you’ll mount them above your window all the way down to where you want the blinds to end (usually just below the sill).
That’s it: smallest inside numbers, biggest outside numbers. Report back if the blinds still try to sabotage you.
Honestly, measuring windows for blinds isn’t rocket science, but you would not believe how many times I’ve gotten it wrong (blinds half-covering the glass, me tripping over the extra, the whole deal). So, while @ombrasilente basically laid out the textbook method, here’s my own two cents and a couple of warnings.
First—yes, figure out if you want inside or outside mount like they said, but don’t just accept whatever the old blinds did as gospel. Sometimes previous owners installed what “kinda fit” instead of what looked or worked best. Stand back. Envision: Do you want to see trim? Are you trying to block out neighbor Steve’s floodlight?
For inside mounts, I actually prefer to round DOWN on the width slightly (like 1/8”) rather than go with the smallest. Why? Because real window frames are almost never perfectly square. You can sand/shim a tiny gap, but you can’t jam a too-wide blind in there. For height, I ignore the tallest and go with the middle value, because the window sill end is usually slightly uneven. The “tallest wins” rule can give you blinds that bunch awkwardly at the bottom. It’s not a huge deal, just my small improvement over the standard advice.
For outside mounts, don’t get suckered into the “just go wider” logic. Measure your trim AND consider if you have wall obstacles (like outlets, baseboard heaters, whatever). Also, don’t forget you need enough flat wall space on each side—found that out the hard way when I tried mounting and realized half the screw holes hit air. Yes, outside mounts can hide ugly framing, but make sure the screws have something solid to bite into.
One more thing no one ever talks about—measure your mounting surface too. Sometimes there are weird bumps, security sensors, mini shelves, or ancient paint globs in the way. Been there.
My final rant: Write your numbers in marker, not pencil, because the only thing worse than measuring twice and cutting once is measuring three times and still squinting at smudged pencil marks. And take pics of your window with your phone too—salespeople actually find it helpful.
In short: Take three sets of measurements, trust but verify, be paranoid about fit, then go drink something while you wait 4-6 weeks for that “in stock” order to actually ship. If you mess up, at least blinds are easier to hide than, say, a crooked shower door.
I’ll jump in here as someone who’s measured windows for blinds way too many times (old houses = endless surprises). It’s wild how folks try to turn this into a mystical art when it’s more like cautious guesswork with a tape and a touch of optimism.
Both previous responses went deep on inside/outside mount decisions—which matters—but let’s talk reality: window frames are rarely square, tape measures lie if you pull them too tight, and daylight makes every error obvious. Here’s an underrated move almost no one mentions: grab a piece of stiff cardboard or a big notepad, physically fit it in the window frame, and mark where it snags or leaves a gap. This exposes the weird bumps nobody’s laser measure will catch. It’ll also help you “see” how your blinds will rest, and is clutch if you’re visual like me.
On the measuring—yep, the smallest width is usually right for inside, and the outside mount should absolutely overhang, but don’t just take numbers. Hold a sample blind (or even a ruler vertically) to the depth and verify clearance for handles or locks. I once skipped this and had gorgeous (useless) blinds that couldn’t close all the way.
Personally, I’m not on board with writing in marker as suggested—if you write on your wall/frame, you’ll regret it when the stains show or you have to return the blinds (been there). Use painter’s tape or sticky notes instead—no mess, no regrets.
About “,” you’re probably wondering whether all this effort’s worth it. Pro: it’s versatile, often fitting cramped frames and offering decent light control. Con: if your windows vary by even a quarter inch, you’ll wish you custom-ordered instead of trusting “one size fits all.” Compared to the approach from @cazadordeestrellas and the more textbook route from @ombrasilente, this product sits in the middle: straightforward install, but be ready for a bit of finagling.
Wild card: measure with your window OPEN, too, if your frame lets in a breeze. Sometimes things shift just enough to mess you up.
In sum: treat your first blind like a test run, use physical mockups, and don’t trust your house to be standard. Only way out is forward—blindly.