How to Measure Roller Blinds for a Proper Fit

A roller blind that is only a few millimetres out can catch on a handle, leave a gap at the edge or sit awkwardly above the window. The good news is that it is straightforward to measure roller blinds accurately when you know which size you are ordering. Take your time, use a steel tape measure and write every figure down in millimetres.

The first decision matters most: is the blind fitting inside the window recess, or over the recess on the wall, ceiling or window frame? These are measured differently. No gimmicks, no guesswork - choose the fitting type first, then measure for that space.

What you need before measuring

Use a steel tape measure rather than a fabric tape. A metal tape stays straight across the opening and gives a more reliable reading. You will also need a pencil, paper and, if possible, a second person for wide windows.

Measure in millimetres, not centimetres. For example, write 1,245 mm rather than 124.5 cm. This avoids misplaced decimal points and makes it easier to enter your measurements when ordering. Measure the window itself, not an old blind. Existing blinds may have been fitted with a gap, cut down or mounted off-centre.

Before you start, look for anything that could affect the blind's position. Window handles, tiles, deep sills, alarm sensors, opening windows and projecting vents can all influence whether a recess or exact fit is best. A blind needs enough room to roll freely, not just enough space for the fabric.

How to measure roller blinds inside a recess

A recess fit sits inside the window opening. It gives a neat, built-in look and keeps the blind close to the glass. It is a popular choice for living rooms, kitchens and bathrooms where there is sufficient depth.

Measure the recess width in three places

Measure the inside width at the top, middle and bottom of the recess. Use the narrowest of the three measurements. Walls and window reveals are not always perfectly square, particularly in older homes, and ordering from the widest point can leave a blind that will not fit.

Measure from one inside edge of the recess to the other. Do not include any tiles, trim or window frame that sits inside the opening unless that is where the brackets will be fixed. Keep the tape level rather than following a sloping sill.

When an order form asks for the recess size, provide the exact smallest width you measured. Do not make your own deduction unless the product instructions specifically tell you to. Made-to-measure recess blinds are normally produced with an allowance for the operating mechanism and clearance, but the finished blind width and fabric width can vary by product. Ordering instructions for the blind you have chosen should always take priority.

Measure the recess drop in three places

Next, measure the drop from the top inside edge of the recess to the sill in three positions: left, centre and right. Use the shortest measurement. This prevents the bottom bar from scraping a sloping sill or catching on a tile edge.

If there is no sill, measure to the point where you want the blind to finish. For a recess blind, most people measure to the bottom of the recess. Check that the bottom bar will clear handles or other fittings when the blind is lowered.

Check recess depth and obstructions

Width and drop are not the only figures that matter. Check the recess depth, especially where there are handles or large hinges. A roller blind has brackets and a tube as well as fabric, so a shallow recess may mean the blind projects beyond the face of the wall.

If a handle sticks out into the blind's path, an exact fit outside the recess is often the more practical option. Alternatively, a small amount of clearance may be acceptable if privacy matters more than blocking every edge of light. For blackout bedrooms, however, a recess fit naturally allows more light around the sides than a wider blind mounted over the opening.

Measuring roller blinds for an exact fit

An exact fit, sometimes called an outside-recess fit, is mounted over the window opening. The brackets can be fixed to the wall, ceiling or face of the window frame, depending on the space available. This fitting is useful when the recess is shallow, the opening is uneven, or you want better coverage around the edges.

Start by deciding exactly where the brackets will go. Then measure the total width and drop you want the completed blind to cover, rather than simply measuring the glass.

For the width, a practical starting point is to allow around 50 mm overlap on each side of the recess. This helps reduce side gaps and improves privacy. A wider overlap can be useful for a blackout blind in a bedroom, while a narrower overlap may be needed if there is a nearby wall, cupboard or light switch.

Take care around opening windows. A blind fitted too close to the frame may prevent a handle from turning or may rub against it every time the window is used. In that case, mount the blind higher above the recess or choose a wider projection from the wall if the bracket position allows it.

For the drop, measure from the point where the top of the bracket will sit down to where you want the bottom bar to finish. Adding around 50 mm above the recess gives room for the roller and helps cover the top of the opening. If there is space, fitting higher can also make a window look taller and gives better light control when the blind is down.

Be clear about the measurement requested by the product. Some roller blinds are ordered by the full bracket-to-bracket width, while the fabric is slightly narrower to allow room for the mechanism. This is normal. Never assume that fabric width and blind width are the same, particularly if you are trying to cover a precise opening.

Common measuring mistakes to avoid

The most common mistake is measuring only once. Check every number before ordering, especially on wide windows where it is easy for the tape to bend. Measuring in three places takes a few extra minutes and can save the cost and delay of replacing a blind.

Another mistake is rounding up. If your recess is 1,202 mm wide, record 1,202 mm, not 1,200 mm or 1,205 mm. Small differences matter in a tight recess. The same applies to the drop.

Do not forget the control side. Decide whether you want the chain on the left or right before ordering. Choose the side that is easiest to reach and least likely to interfere with a handle, cupboard or furniture. Keep chains safely secured with the supplied safety device, particularly in homes with young children.

Finally, do not choose a fitting type based on appearance alone. A recess blind looks tidy, but it depends on adequate depth and a reasonably square opening. An exact fit can cover more light and work around awkward windows, though it will sit proud of the wall. The right choice depends on your window and how you use the room.

Measuring different rooms

Bathrooms and kitchens often suit wipe-clean PVC waterproof roller blinds, but check for tiles inside the recess. Measure between the narrowest points, as tiles can make an opening tighter near the bottom than at the top. For an outside-recess fit over tiles, make sure the chosen fixing position is suitable for the wall surface.

For bedrooms, consider how much light you want to block. A blackout fabric reduces light through the material, but light can still appear around the sides of any standard roller blind. A wider exact fit with a generous overlap usually gives better coverage than a recess fit.

In rented homes, check what fixings are permitted before choosing a wall or ceiling fit. If you are replacing an existing blind, measure the intended new blind rather than relying on the old bracket positions. This is particularly useful when refreshing worn window coverings without replacing every part of the room.

Once your measurements are written down, check them against the fitting guidance for your chosen blind one final time. Accurate measuring is the simplest route to a made-to-measure blind that looks right, works properly and earns its place at the window.