What Size Blind Should I Buy?

A blind that is 1 cm out can look wonky, catch on the handle, or let in more light than you expected. So if you're asking, what size blind should I buy, the right answer starts with how your window is fitted, not just the width of the glass.

Getting the size right is what makes a blind look neat and work properly. It affects privacy, blackout performance, how smoothly the blind operates, and whether it sits cleanly inside the recess or covers it properly from the outside. The good news is that measuring is straightforward once you know what you are measuring for.

What size blind should I buy for your window?

The first thing to decide is whether you want an inside recess fit or an exact fit outside the recess. This changes the size you need to order.

A recess fit means the blind sits inside the window recess. This is the most common choice when you want a tidy, built-in look. For this, you measure the width and drop of the recess, not the glass. Measure in centimetres, and take each measurement in three places - top, middle and bottom for width, then left, centre and right for drop. Use the smallest measurement in each case. Window recesses are not always perfectly square, even in newer homes.

An exact fit means the blind sits outside the recess, covering the window area and usually overlapping it. This works well if the recess is too shallow, there are obstructions inside it, or you want better blackout coverage. In this case, measure the area you want the blind to cover, then add extra width and drop so the blind overlaps the recess. A common rule is to add around 5 cm to 10 cm on each side where space allows, but it depends on handles, nearby walls, radiators and how much coverage you want.

How to measure before you buy

Use a metal tape measure rather than a cloth one. Cloth tapes can flex and give you a less accurate reading. Measure to the nearest millimetre if possible, even if you plan to enter the size in centimetres when ordering.

For recess measurements, check the depth as well as the width and drop. Some blinds need enough room for brackets, fabric roll or slats to operate freely. If the recess is shallow, an outside fit may be the better option.

Also look for anything that could interfere with the blind. Window handles, trickle vents, tiles, sills that project out, and inward-opening windows can all affect the fit. A blind that looks right on paper can still be awkward if a handle pushes the fabric forward or stops it dropping straight.

If you are measuring for more than one window, measure each one separately. Two windows that look identical are often slightly different in size. Guessing based on one measurement is a quick way to end up with one blind that fits and one that does not.

Recess fit or exact fit?

If you want the blind to sit neatly within the frame, go for recess fit. It keeps the blind contained and often suits living rooms, kitchens and bathrooms where a cleaner line matters more than complete blackout. It also works well when there is enough depth in the recess for the blind to operate properly.

If light control is the priority, exact fit often gives better coverage. Because the blind overlaps the recess, there is less gap at the sides. This matters in bedrooms, especially with blackout roller blinds. You may still get some light around the edges, but generally less than with a recess fit.

Neither option is always better. It depends on the room, the window shape, and what matters most - appearance, blackout, or working around obstructions.

What size blind should I buy for different blind types?

The style of blind affects sizing as well. Roller blinds, vertical blinds and replacement slats are measured differently enough that it is worth checking the product type before ordering.

Roller blinds are usually the simplest. For a recess fit, you measure the recess width and drop. For an outside fit, you choose the finished size you want the blind to cover. Keep in mind that the fabric width is often slightly narrower than the full blind width because of the mechanism and brackets. That is normal, but it matters if you are trying to minimise side gaps.

Vertical blinds suit wider windows, patio doors and larger openings. If you are replacing a full vertical blind, measure the full width and drop of the area to be covered. If you are only replacing slats, the slat width and slat drop must match the existing system. In that case, measuring one existing slat is usually the safest route rather than estimating from the window size.

Blackout blinds need a bit more thought. If your main concern is reducing light in a bedroom or nursery, a recess fit can still work, but exact fit usually gives better results because you can add overlap around the window. It is a practical trade-off between the neatest look and the best blackout performance.

PVC waterproof blinds are often chosen for kitchens and bathrooms. Here, exact fit can be useful if tiles, sills or limited recess depth make inside fitting awkward. These blinds are also popular in rentals because they are easy to wipe clean and simple to maintain.

Common sizing mistakes that cause problems

Most blind sizing errors come from measuring the wrong area or assuming too much. Measuring only the glass is one of the biggest mistakes. Unless you are fitting to the glass itself, which is unusual for standard blinds, you need the recess or the full coverage area.

Another common problem is ignoring handles. A blind may fit inside the recess but sit badly because the handle pushes against the fabric or slats. Sometimes the fix is choosing an outside fit. Other times, a little extra projection from the brackets is enough. The key is spotting the issue before ordering.

People also forget that blackout does not just depend on fabric type. A blackout fabric can still let in light at the edges if the blind is too narrow or fitted inside a wide recess. If you are expecting a darker room, sizing and fit matter just as much as material.

Then there is the issue of rounding up. With recess fit blinds, ordering slightly bigger is not playing safe. It is often the opposite. If the blind is too wide for the recess, it simply will not fit properly. Accurate measuring matters more than guesswork.

Made to measure or ready made?

If your window happens to match a standard ready-made size, that can be a quick option. But many UK windows do not fall neatly into off-the-shelf widths, especially in older properties, extensions and rented homes where fittings may have changed over time.

Made-to-measure blinds remove a lot of the compromise. You order the size your window actually needs rather than the nearest standard option. That usually means a better fit, fewer gaps, and less chance of drilling twice because the first blind was not quite right. For landlords and homeowners replacing tired blinds room by room, that can save time as well as money.

This is also where product choice matters. If you need blackout for a bedroom, waterproof PVC for a bathroom, or just replacement vertical slats rather than a full new blind, getting the size right is what makes the purchase worthwhile. Queen Blinds focuses on that practical side of custom ordering - fit first, then finish.

A simple way to decide the right blind size

Start with the room. If it is a bedroom and light control matters, consider an exact fit with enough overlap to reduce gaps. If it is a kitchen or bathroom with limited recess space, check for tiles, handles and moisture, then choose a fit and material that suits the space. If it is a living room and you want a tidy built-in look, recess fit is often the obvious choice.

Then measure properly, once for width and once for drop, in more than one place. Use the smallest recess measurement if fitting inside. Use your chosen finished coverage size if fitting outside. Check depth, handles and any obstacles before you order.

Blind buying does not need to be complicated, but it does need to be exact. Get the measuring right, and the rest becomes much easier - the blind will hang better, look better, and do the job you bought it for.