Recess fit sits the blind inside the window opening for the neatest look, exact fit takes the blind to precise brackets you specify yourself, and outside-recess fit mounts the blind on the wall around the opening for extra light coverage. Whichever you choose, measure the width and height in three places, not one, and use the smallest figure. Wrong measurement is the most common support call in the blinds industry, and it happens because window recesses, especially in older housing stock, are rarely perfectly square.

 

Key takeaways

• Measure width and height in three places each, top, middle, bottom for width and left, middle, right for height, then use the smallest measurement across all three.
• A Victorian or Edwardian recess can vary by well over a centimetre from one side to the other. This is normal for period housing, not a building fault.
• Recess fit blinds sit inside the window opening. Outside-recess fit blinds are mounted on the wall or frame around the opening, typically overlapping the recess by 35 to 100mm on each side depending on the retailer and how much light coverage you want.
• A recess depth of 60mm or less, or a window that opens inward into the recess, usually rules out a recess fit and needs an outside-recess mount instead.
• BS EN 13120, the UK’s blind cord safety standard, applies regardless of how the blind is measured or mounted. Cord clearance and breakaway device requirements are the same for recess, exact and outside-recess fittings.

 

What Do Recess, Exact and Outside-Recess Actually Mean?

These three terms describe where the blind physically sits in relation to your window opening, and getting the wrong one is the single biggest cause of a blind that doesn’t fit properly.

Recess fit

means the blind is mounted inside the window recess, the hollow space between the glass and the front of the wall. This gives the neatest, most integrated look, since the blind sits flush with the wall and doesn’t project into the room. A small deduction is made automatically to the measurement you give, so the blind clears the sides of the recess and operates smoothly.

 

Exact fit

means you are specifying the finished size of the blind yourself, including all brackets and hardware, with no automatic deduction made. This is used either when replacing an existing blind of a known size, or when mounting a blind on the face of the window frame rather than inside the recess.

 

Outside-recess fit

(sometimes called face fit) means the blind is mounted on the wall or frame around the outside of the recess, overlapping the opening on all sides. This is the option you need if the recess is too shallow to hold a bracket, if there’s an obstruction inside the recess such as a window handle, or if you want extra overlap for better light coverage.

 

 

Why Three Measurements, Not One?

This is the detail almost every DIY measuring guide skips past quickly, and it’s the single biggest reason a blind arrives and doesn’t sit right.

A window recess is not a perfect rectangle, even in a modern new build, and it’s rarely close to one in a Victorian or Edwardian terrace. Recesses settle over decades, plaster shifts, and in a lot of period housing stock across East London, Dagenham, Ilford, Walthamstow and the surrounding boroughs, the recess was never built perfectly square in the first place, because the construction tolerances of the time were nowhere near what’s standard today.

If you measure the width once, usually across the middle, and assume that figure holds for the whole height of the recess, you’re gambling on the recess being uniform. It often isn’t. Measure the width at the top, in the middle and at the bottom, then measure the height on the left, in the middle and on the right. Take the smallest of the three width measurements and the smallest of the three height measurements, since ordering to the largest figure risks a blind that’s too wide or too long to sit inside the recess cleanly.

This single step is why a professional measuring visit exists as a service at all. It isn’t about the tape measure, it’s about knowing to take three readings, spotting when a recess is out of square before it becomes a fitting problem, and choosing recess, exact or outside-recess based on the actual depth and shape of your specific window rather than a general assumption.

 

How to Measure for a Recess Fit Blind

Measure the width of the recess at three points, top, middle and bottom, using a metal tape measure rather than a cloth one, since cloth tapes stretch slightly and introduce inaccuracy. Record all three figures and use the smallest.

Measure the height (also called the drop) at three points, left, middle and right, from the top of the recess down to the sill or bottom of the opening. Again, record all three and use the smallest.

Check the depth of the recess before committing to a recess fit. Most blind types need at least 60 to 75mm of clear depth to mount the brackets and allow the blind to operate without catching on the window handle, hinges or any other obstruction. If your recess is shallower than this, or if the window opens inward into the recess space, a recess fit generally isn’t practical and an outside-recess fit is the better option.

 

How to Measure for an Outside-Recess Fit Blind

Decide how far you want the blind to overlap the recess on each side. Retailers vary in their recommendation here, typically somewhere between 35mm and 100mm per side depending on how much light coverage you’re after, but the principle is consistent: more overlap means less light leaking in at the edges, particularly relevant for a bedroom or nursery where you want a genuinely dark room.

Measure the width you want the finished blind to cover, from where you want the left edge to sit to where you want the right edge to sit, factoring in your chosen overlap on both sides.

Measure the height the same way, from where you want the headrail to sit down to where you want the bottom of the blind to finish, again factoring in any overlap you want at the top and bottom.

Check for obstructions. A radiator, a picture rail, tiling, or a windowsill that protrudes further than the wall above it can all affect where you’re able to mount an outside-recess blind, so measure with these in mind rather than assuming a clear, flat wall surface.

 

Measuring for a Bay Window

A bay window needs a different approach entirely, because it isn’t one flat opening, it’s two, three or more panes set at angles to each other. Every pane needs its own set of measurements, taken individually, not averaged or assumed to match its neighbours.

For a square or slightly splayed bay, the straight sides typically get ordered as recess fit blinds, while the angled corner panes often need to be ordered as exact or outside-recess fit to allow for the angle and any obstruction where the panes meet. This is genuinely fiddly to get right without experience, since the angle of a bay in a Victorian terrace is rarely a clean, textbook angle, and getting even one pane wrong throws off the whole set. This is exactly the kind of job where a professional measuring visit earns its keep, since the person measuring has done dozens of East London bays and knows what to check for before an order goes anywhere near production.

 

What Goes Wrong When Measuring Is Done Incorrectly

Measuring the recess once instead of three times.

The most common mistake. A blind ordered to a single measurement that doesn’t account for an out-of-square recess will be too wide at one point and too narrow at another, meaning it either won’t fit at all or won’t sit flush.

 

Confusing recess and exact sizing.

Submitting a recess measurement when the blind actually needs to be ordered as exact, or vice versa, results in a blind that’s either too big to fit inside the recess or too small to cover the opening properly. This mix up is a genuinely common support call, and it stems from the terminology being confusing to anyone ordering blinds for the first time.

 

Not checking recess depth before choosing recess fit.

A recess under roughly 60mm deep, or one with a window that opens inward, usually can’t accommodate a recess mounted blind’s bracket and mechanism. Ordering recess fit anyway typically means the blind won’t operate correctly, or won’t fit at all.

 

Ignoring obstructions.

Window handles, hinges, alarm sensors, and inward opening panes all reduce the usable depth or width of a recess. A measurement that doesn’t account for these ends up with a blind that catches or can’t close fully.

 

Measuring for a bay window as if it were one flat opening.

Treating a bay as a single wide window rather than several individually angled panes is one of the most common and most visible mistakes, since the result is a set of blinds that don’t sit flush at the angled joins.

 

Recess vs Exact vs Outside-Recess: Which Should You Choose?

Situation	Best measuring approach	Why	Watch out for
Standard window, recess 75mm+ deep, no obstructions	Recess fit	Neatest, most integrated look, sits flush with the wall	Recess must be genuinely square-ish and deep enough
Recess under 60mm deep, or window opens inward	Outside-recess fit	Recess fit won’t have room to operate properly	Needs a flat wall surface around the opening to mount to
Bedroom or nursery needing genuine blackout	Outside-recess fit, generous overlap	Extra overlap closes the light leak gap at the edges	Overlap needs checking against nearby obstructions like a radiator
Replacing an existing blind, same size	Exact fit	You already know the finished size needed, no deduction wanted	Measure including all existing brackets and fittings
Bay window, straight sides	Recess fit per pane	Each straight pane can usually sit inside its own recess cleanly	Still needs individual measuring, not one figure for the whole bay
Bay window, angled corner panes	Exact or outside-recess fit per pane	Angled panes often can’t sit flush inside a recess	The angle itself needs measuring accurately, not estimated
Tiled recess or picture rail interrupting the opening	Outside-recess fit, or narrowest point recess fit	Tiling or trim can narrow the usable recess partway down	Measure from the tiled section if it’s narrower than the top

 

What “Exact Blind Size” Actually Includes

A common confusion when measuring for an outside-recess or exact fit is what the final figure is supposed to cover. The exact blind size is the full finished width and height, including the headrail, brackets and any end caps, not just the width of the fabric itself. For a roller blind, the fabric typically sits a few centimetres narrower than the overall bracket to bracket width, since the mechanism at each end takes up space beyond the visible fabric edge. For a Venetian blind, the same principle applies to the headrail and bottom bar. If you give us the fabric width instead of the full exact size, or the other way round, the finished blind can end up narrower or wider than intended, which is exactly the kind of mix up a professional measuring visit avoids.

 

Measuring for Roof Windows and Velux Blinds

Roof windows need a different measuring approach entirely, because the blind fixes directly into the window’s own glazing bar system rather than a wall recess. Rather than measuring a recess, you’re generally identifying the exact model and size of your roof window, since Velux, Fakro, Keylite and other manufacturers each use a specific reference code for their window sizes, and the blind is made to match that code precisely. Guessing a roof window measurement the way you might a standard wall recess doesn’t work reliably, since a blind that’s a few millimetres out on a roof window won’t seal against the frame and will leak light around the edges, defeating much of the point of fitting one.

 

Who Should Measure Their Own Blinds

Anyone replacing an existing blind with one of the same size and type, where the finished dimensions are already known and there’s no recess shape or squareness to assess. Anyone fitting a single, standard rectangular window with a clear, deep recess and no obstructions is also generally fine measuring their own, provided the three-point method above is followed carefully.

 

Who Shouldn’t Measure Their Own Blinds

Anyone with a bay window, since the angled panes and individual measurements needed make this genuinely easy to get wrong without experience. Anyone in a Victorian, Edwardian or older property where the recess is visibly, or even subtly, out of square. Anyone unsure whether their recess is deep enough for a recess fit, since guessing wrong here means ordering the wrong product entirely. And anyone who wants a genuinely dark bedroom, since getting the overlap calculation right for true blackout is easy to underestimate without professional experience of how much light actually leaks around a given fit.

 

 

Why We Offer Free Measuring as Standard

Given how often measuring goes wrong, and how much of that comes down to recess squareness, depth and bay window angles that aren’t obvious without experience, we measure every job ourselves as part of our free service across East London and Essex. We measure in three places as standard, check recess depth and squareness before recommending recess, exact or outside-recess fit, and measure bay windows pane by pane. This is included with every order, whether it’s a single kitchen window or a full house.

 

How to Measure for Blinds FAQ

1. Do I need to measure my own blinds if London Blinds 4U offers free measuring?
   No. Our free measuring service is included with every order, and we’d generally recommend it over DIY measuring, particularly for bay windows or older properties where recess squareness is harder to judge without experience. This guide is here for anyone who wants to understand the process, or who’s comparing quotes and wants to know what to expect.
2. What’s the difference between recess and exact sizing?
   Recess sizing means you give us the size of the recess opening and a small deduction is made automatically so the blind fits and operates cleanly inside it. Exact sizing means you specify the finished size you want, including brackets, with no deduction made. Exact is used for outside-recess mounting or when replacing an existing blind of a known size.
3. Why do I need to measure in three places?
   Because window recesses, particularly in older properties, are rarely perfectly square. Measuring in one place only risks missing a variation between the top, middle and bottom of the recess, which can result in a blind that’s too wide at one point and doesn’t sit flush.
4. How deep does my recess need to be for a recess fit blind?
   Most blind types need at least 60 to 75mm of clear depth to mount properly and operate without catching on window handles or hinges. If your recess is shallower than this, an outside-recess fit is usually the better option.
5. How much should a blind overlap the recess for an outside-recess fit?
   This varies, typically between 35mm and 100mm per side, depending on how much light coverage you want. More overlap means less light leaking in at the edges, which matters most for a bedroom or nursery where genuine darkness is the goal.
6. Can I measure a bay window myself?
   You can, but it’s genuinely easy to get wrong. Each pane in a bay needs its own individual measurement, and the angled corner panes in particular are difficult to measure accurately without experience. We’d recommend a free measuring visit for any bay window.
7. What happens if my measurements are wrong?
   The blind may not fit the recess, may not sit flush, or may not operate correctly if it catches on an obstruction. This is why professional measuring exists as a service, since it removes the risk of a costly reorder.
8. Do I need a metal tape measure or will a cloth one do?
   A metal tape measure is strongly recommended. Cloth tapes can stretch slightly under tension, which introduces small inaccuracies that matter more than they might seem, particularly on a recess fit where the tolerances are tight.
9. Does the measuring method change for shutters?
   Broadly the same principles apply, recess, three point measuring, and checking squareness, though shutters have an additional check: the recess needs to be genuinely close to square, since a rigid shutter frame can’t accommodate the kind of out of square recess that a soft blind fabric can flex around slightly. If you’re considering shutters for an older property, a professional measuring visit is particularly worthwhile.
10. How much does it cost to have blinds professionally measured?
    Please call or WhatsApp us on 07852 257 307 for a price. Our measuring and fitting service is offered as part of the overall quote for your blinds or shutters, and we’re happy to talk you through exactly what’s included before you book a visit.
11. Do you offer free measuring across all of East London?
    Yes, our free measuring and fitting service covers East London and Essex, including Dagenham, Barking, Ilford, Romford, Stratford, Walthamstow, East Ham, Leyton, Forest Gate, Canning Town, Poplar, Docklands, Canary Wharf, Hackney, Chadwell Heath and Barkingside, along with the surrounding areas.