How to Measure for Roman Blinds for a Perfect Fit

Before you even think about measuring, let's get your gear sorted. Trust me, spending a few minutes on preparation is the secret to a flawless fit, especially if you're dealing with a window that has a bit of character. Getting this part right from the start will save you a world of frustration later on.

Your Essential Measuring Toolkit

First things first, you need a good quality, metal tape measure. Forget about the soft, fabric kind a tailor might use; they can sag and stretch, which is the last thing you want when precision is key. A metal tape gives you that rigid, straight line needed for a truly accurate reading across the width and drop of the window.

Make sure your window area is completely clear. That means taking any plants or ornaments off the windowsill and shifting any furniture that's blocking your access. You need to be able to get right up to the frame without anything getting in your way.

Next, have a pencil and paper ready. I know it sounds obvious, but you’d be surprised how many people try to remember the numbers in their head.

Here’s a pro tip: quickly sketch the window on your paper. As you take each measurement, jot it down on the corresponding part of your drawing straight away. This little habit is a lifesaver and helps avoid the classic pitfall of mixing up width and height.

With your tools in hand and a clear space to work, you're all set to begin. If you're still deciding on the perfect style, seeing them in person can make all the difference. You can always find the best blinds showroom near me to explore different fabrics and get some hands-on advice.

Measuring for an Inside Mount Recess Fit

An inside mount, what we often call a 'recess fit', is a brilliant choice for a clean, modern look. The blind sits snugly inside the window frame, creating a minimalist profile. This sleek finish, however, depends entirely on precise measurements – there’s simply no wiggle room.

First things first, let's get the width of your window recess. Grab your metal tape measure and measure the full distance from one side of the internal frame to the other. To get this right, you’ll need to take this measurement at three different points.

Finding Your True Recess Width

Window frames are rarely perfectly square, especially in older homes. This is why taking three separate measurements isn't just a suggestion; it’s essential for a blind that operates smoothly.

• Measure the top: Run your tape across the very top of the recess, exactly where the headrail will sit.

• Measure the middle: Next, take a measurement across the centre of the window opening.

• Measure the bottom: Lastly, measure the width right down near the windowsill.

Jot down all three figures. Now for the most important step: always use the smallest of the three measurements. For instance, if you measured 905mm, 903mm, and 908mm, the number you'll use is 903mm. This guarantees the blind won’t catch on the narrowest part of the frame as it moves.

Taking the smallest measurement is the single best trick to avoid a poorly fitting blind. A blind that's even a few millimetres too wide will scrape against the frame and won't operate properly.

Checking the Recess Drop

Now, you're going to do the exact same thing for the height, or what we call the 'drop'. Measure the height of the recess from the top surface inside the frame right down to the windowsill.

• Measure the drop on the left side.

• Measure the drop in the centre.

• Measure the drop on the right side.

Just as before, you’ll take the shortest of these three measurements as your final drop. Given the character of the UK’s housing stock, slight variations in window openings are the norm, which is why following this measuring advice is so crucial. If you're curious, you can find more insights about the UK blinds market.

By taking this careful, methodical approach, you're giving your supplier the exact recess dimensions. They will then make the small, professional deductions needed to make sure the blind fits and operates flawlessly within the tightest points of your window frame.

Measuring for an Outside Mount Exact Fit

An outside mount, what we in the trade often call an 'exact fit', is the go-to solution when you need to really block out the light or want to disguise a less-than-perfect window frame. Instead of sitting neatly inside the recess, this blind is mounted on the wall surrounding the window, so you’ll be adding to your window's dimensions.

The big decision here is how much you want the blind to overlap the window. A great starting point is to add at least 7-10cm (that's about 3-4 inches) to each side—left, right, top, and bottom. This overlap is what stops that frustrating light bleed around the edges, giving you total privacy. It's the secret to a truly effective blackout blind in a bedroom.

Deciding Your Overlap

Of course, that 7-10cm is just a guideline. You have complete control here, and you can play with the overlap to get different looks.

For example, a wider overlap can make a window feel much grander than it actually is—a classic interior design trick. This works wonders, and you can find more ideas like this in our guide on choosing the best blinds for large windows.

On the other hand, you might be working with a window that's tight against a wardrobe or wedged between two walls. In that case, you’ll need a much smaller, more precise overlap. That’s the beauty of an exact fit; you tailor the final size to your specific space.

Taking Your Final Measurements

With an exact fit, you're not measuring the window—you're deciding the final, finished size of the blind itself.

• For the width: Measure the full width of your window recess, then add your chosen overlap to both sides. So, if your window is 100cm wide and you want a 7cm overlap, your final blind width will be 114cm (100 + 7 + 7).

• For the drop: Follow the same logic for the height. Measure from the top of the opening to the bottom, then add your desired overlap above the frame and below the sill.

One final check before you commit: Stand back and scan the wall around the window. Are there any obstacles? Look for things like dado rails, deep skirting boards, radiators, or even chunky window handles that could prevent the blind from hanging and operating smoothly.

Taking a moment to spot these potential snags is a simple step that can save a world of frustration on installation day. It ensures your new Roman blind will look and work exactly as it should.

Handling Bay and Corner Windows

Bay windows can be the centrepiece of a room, but they often leave people scratching their heads when it comes time to measure for blinds. The secret? Stop seeing it as one big, awkward window. Instead, think of it as three (or more) separate windows that just happen to be joined together.

The whole game is won or lost in the corners where the blinds meet. You need to make absolutely sure the headrails—the top part that houses all the mechanisms—can sit next to each other without clashing. If they knock together, your blinds simply won't operate smoothly, and you'll be stuck with a frustrating and expensive mistake.

Measuring Angled and Square Bays

For a standard angled bay, start by finding the exact meeting point in each corner. From this point, measure outwards along the central window to where you want that blind to finish. This gives you the width for your main, centre blind.

Then, go back to that same corner point and measure along the side window to find the width for the side blind. The key here is to remember to factor in the depth of the headrail itself, as it will project out from the frame.

Pro Tip: If you're struggling to visualise the angles, grab a piece of cardboard and cut it to the depth of the headrail. You can then physically place this template in the corner to see exactly how the headrails will sit next to each other. It’s a simple trick I’ve used countless times, and it has saved me from some serious measuring blunders.

Getting that seamless, professional finish all comes down to consistency. For a little more inspiration, take a look at these stunning window dressing ideas for bay windows.

This handy visual guide walks you through the key steps for an outside mount, which is often the best choice for creating that flowing, uninterrupted look across a bay.

As you can see, the first crucial step is always deciding on your overlap before you even pick up the tape measure. A little bit of planning at the start makes all the difference.

Common Measuring Mistakes to Avoid

Even with the best intentions, a few simple slip-ups can lead to a poorly fitting blind. Having seen every possible mishap over the years, we want to help you sidestep these common pitfalls. Think of this as your essential checklist to guarantee a flawless result on your first attempt.

One of the most frequent errors we see is accidentally mixing up the width and height. After measuring a few windows, it’s surprisingly easy to jot down 1200mm x 1800mm when you really meant the reverse. A simple habit to get into is always labelling your sketch clearly with ‘W’ and ‘H’ next to the numbers. It’s a tiny detail that prevents a major headache.

Another tempting shortcut is to measure an old blind instead of the window itself. Please don't do this. Fabric can stretch, shrink, or distort over time, meaning the old blind is no longer a true reflection of your window's actual dimensions. Always measure the recess or the wall space you intend to cover.

The Golden Rules of Measuring

You’d be amazed how often windows that look identical are actually a few crucial millimetres different, especially in older properties. This is precisely why you must measure every single window individually. Never assume they are the same size; that assumption is the fastest route to a blind that simply won’t fit.

When you're ordering for a recess fit, it's vital that you provide the exact, tight measurements of the window opening.

Do not make any deductions yourself. We are experts at calculating the precise reduction needed for the brackets and smooth operation. Giving us the tight recess size allows us to manufacture a blind that fits perfectly within the space.

By avoiding these common mistakes, you’re not just learning how to measure correctly; you’re saving yourself the time, money, and frustration of getting it wrong. Double-check everything, take your time, and you'll be rewarded with a beautiful, custom-fit result.

Got a Few More Questions About Measuring?

Even with the best instructions, a few tricky situations can pop up. Let’s tackle some of the most common questions I hear from customers to make sure you’re ready for anything.

What If My Window Handle Sticks Out?

This is a classic problem, especially with older uPVC or timber windows. If you’re hoping to fit the blind inside the recess, that handle could get in the way.

First, check the depth of your window recess. Every Roman blind has a minimum depth it needs to hang freely – you'll find this on the product's specification page. If your recess is deep enough for the blind to clear the handle, you’re good to go.

If it’s too shallow or the handle is particularly chunky, the simplest solution is to mount the blind on the outside of the recess. This way, it hangs in front of the window frame, completely avoiding the handle.

Do I Need to Take Any Millimetres Off for a Recess Fit?

Absolutely not! This is a crucial point: when you order for a recess fit, you should provide the exact, wall-to-wall measurements. Don't be tempted to knock a bit off yourself.

Our workshop team are the experts here. They know precisely how much space to deduct – usually about 1cm from the total width – to account for the brackets and ensure the blind operates smoothly without snagging. Give us the tight, true size, and we’ll handle the rest.

Should I Measure in Centimetres, Millimetres, or Inches?

For made-to-measure blinds, precision is everything. That’s why we, along with most UK suppliers, work exclusively in millimetres (mm).

Measuring in millimetres gets rid of any confusion that can come with fractions of an inch and gives us the most accurate information to create your blind. It’s the industry standard for a reason and the best way to guarantee a perfect, snug fit.

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For a perfect fit every time, explore the bespoke collection at Blindsmart. Our expert team on the Isle of Man is ready to help you find the ideal solution for your home. Visit us online at https://www.blindsmart-im.co.uk.