A roller blind can make a bay window feel calm and considered, or give a bedroom the darkness needed for a proper night’s sleep. The difference often comes down to a few millimetres. Knowing how to measure roller blinds correctly helps ensure the blind sits neatly, rolls smoothly and provides the level of privacy or light control you expect.
Before reaching for a tape measure, decide whether the blind will sit inside the window recess or outside it. This single choice affects every measurement that follows, as well as the finished look of the room.
Choose between recess and face fitting
A recess fit positions the roller blind within the window opening. It is a tidy, understated choice that keeps the blind close to the glass and works especially well where there is enough depth for the brackets and fabric roll. It can also leave a sill clear for plants, ornaments or practical everyday use.
A face fit, sometimes called an exact fit, places the blind outside the recess. The brackets are fixed to the wall above the window, to the ceiling, or occasionally to the window frame. This approach gives greater coverage around the edges of the window and is often the better option for blackout blinds, shallow recesses, outward-opening windows or windows with obstructions inside the reveal.
There is no universal right answer. Recess fitting offers a tailored, built-in appearance, while face fitting can improve light reduction and conceal an uneven or awkward recess. Consider how the room is used as well as how you would like the window treatment to look.
What you need before measuring roller blinds
Use a quality metal tape measure rather than a fabric tape, which can stretch and make accurate readings harder to achieve. A pencil and notepad are useful, even if you are measuring only one window. Record each dimension immediately and label it clearly by room and window.
Measure in millimetres wherever possible. This gives the most precise result and avoids confusion between centimetres and millimetres when ordering a made-to-measure blind. Do not rely on measurements from property plans or estimate from an existing blind. Windows are rarely as uniform as they appear, particularly in period homes.
It is also worth checking for anything that may interfere with the blind. Window handles, trickle vents, tiles, dado rails, deep glazing bars and alarm sensors can all influence the best fitting position. Open the window fully where possible and think about access to handles once the blind is in place.
How to measure roller blinds for a recess fit
For a recess-fitted roller blind, measure the inside of the window opening in three places for both width and drop. Take the width across the top, middle and bottom of the recess. Then measure the drop on the left, in the centre and on the right.
Use the smallest width measurement and the shortest drop measurement. Recesses can taper slightly, and choosing the smallest figures gives the blind sufficient clearance to operate without catching on the sides or sill.
Measure from the inside edge of the recess, not from the glass or the window frame. Keep the tape measure straight and level, rather than following an uneven plaster line. If the recess has tiles, a projecting sill or any decorative trim, measure the usable opening where the blind will actually sit.
Check recess depth before ordering
Width and drop alone do not tell the whole story. Roller blind brackets and the fabric roll need enough room in front of the glass. A shallow recess may cause the blind to project beyond the opening, while handles or vents can prevent it from hanging freely.
Measure the available depth from the front edge of the recess to the nearest obstruction. This is particularly relevant for blackout fabrics, which may be paired with side channels or a cassette, and for double roller blinds with two fabrics on one bracket system. If depth is limited, face fitting may provide a cleaner and more practical result.
Remember that the stated blind width can refer to the bracket-to-bracket size rather than the fabric width. The fabric is usually slightly narrower to allow the operating mechanism to turn. This creates small light gaps at either side, which are normal with a standard recess-fitted roller blind.
How to measure roller blinds for face fitting
For a face-fitted blind, start by deciding the coverage you want around the window. Measure the width of the area you wish to cover, rather than the inside of the recess. In most cases, allowing an overlap on both sides of the recess improves privacy and reduces the strips of light that can enter around the fabric.
A common allowance is around 50 mm to 75 mm on each side, provided there is clear wall space. The ideal overlap depends on the room, window position and nearby features. A narrow gap between two windows may limit the width available, while a bedroom may benefit from more generous coverage for a darker finish.
Next, measure the drop from the chosen bracket position to the point where you want the fabric to finish. This may be the sill, just below it, or down to the floor for a full-length treatment. Add space above the recess so the brackets and roll sit clear of the opening. This helps the fabric cover the glass properly when lowered.
If fitting to a ceiling or into a bay, measure carefully from the exact fixing line. Check that the blind will not strike a radiator, window handle or furniture when pulled down. For a face fit, use the full measurement you want the finished blind to cover. Do not make deductions unless the product specification or your supplier expressly asks for them.
Account for controls, roll direction and everyday use
The chain control can usually be placed on either the left or right. Choose the side that is easiest to reach and least likely to interfere with furniture, curtains or opening windows. In a child’s bedroom or family area, ensure the finished blind will include an appropriate chain safety device and that the chain position can be secured safely.
You may also be asked whether you prefer a standard roll or reverse roll. With a standard roll, the fabric comes off the back of the tube, closer to the glass. This can be useful within a recess. With a reverse roll, the fabric falls from the front of the tube, which may help it clear handles and can create a more decorative appearance when the blind is raised.
Neither option is purely aesthetic. Where the window has prominent handles, a reverse roll may prevent the fabric from brushing against them. In other situations, a standard roll can sit more discreetly. It depends on the depth of the recess, the style of the blind and how the window is used.
Measuring for blackout roller blinds
A blackout fabric blocks light through the material, but standard roller blinds still have natural gaps around their edges. For a room where darkness matters, such as a nursery, bedroom or media room, face fitting is often preferable because it enables wider and higher coverage.
Allow enough fabric to overlap the recess at both sides and above the top edge. Consider whether light may also enter beneath the blind, particularly where there is a deep sill or the blind stops above floor level. Side channels, cassette systems and carefully selected fitting positions can further improve the blackout effect, although the best solution depends on the window construction.
Do not assume that a blackout fabric alone will create complete darkness. The fitting method, fabric coverage and surrounding light all play a part. A considered survey avoids disappointment and produces a more polished result.
Common measuring mistakes to avoid
The most frequent error is supplying the largest recess measurement rather than the smallest. Even a slightly uneven reveal can make a blind too tight to fit properly. Another is measuring only once. Taking each dimension in three places takes very little extra time and can prevent an expensive mismatch.
Avoid measuring from an old blind unless you are certain it fits exactly as intended. Its size may have been chosen to conceal a previous problem, or it may simply be poorly fitted. Equally, do not forget to allow for tiles, handles and projections that sit in the blind’s path.
Finally, clarify whether you are being asked for the finished blind size, the fabric size or the recess size. Made-to-measure suppliers work to different conventions. A professional will explain which figures they need and apply the appropriate manufacturing tolerances.
For homeowners who want the reassurance of an expert eye, a professional measure can be particularly worthwhile for bays, large expanses of glazing, blackout rooms and unusual window shapes. Sunshades Shutters can assess the practical details alongside fabric, colour and finish, so the result feels as good to use as it looks. A precisely measured roller blind is a small detail that brings everyday comfort, privacy and calm to the whole room.