A beautifully dressed window begins long before fabric is chosen or a finish is selected. To measure windows for blinds correctly, you need more than a rough width and drop: you need to decide how the blind should sit, how it will operate, and what will make the room feel considered rather than compromised.

For a made-to-measure result, take your time, use a metal tape measure and record every figure in millimetres. A few millimetres can make the difference between a tailored finish and a blind that catches, gaps or feels visually out of balance.

First, choose recess or outside fitting

The first decision is whether your blind will sit inside the window recess or overlap it on the wall or frame. This choice affects both the measurements and the final character of the room.

A recess fit is positioned within the existing window opening. It is a refined choice for well-proportioned windows, particularly where you want clean lines and wish to retain the detail of an elegant surrounding wall. Recess-fitted blinds work especially well in kitchens, studies and contemporary living spaces where a neat, architectural finish is desired.

An outside fit, sometimes called an exact fit, is installed beyond the recess. This can make a smaller window appear larger, disguise an uneven recess and improve light control by creating a generous overlap around the opening. It is often the more forgiving option for older properties, where walls and window reveals may not be perfectly square.

There is no universally better choice. A deep, crisp recess may call for an inset blind; a bedroom requiring more darkness may benefit from an outside fit with a wider overlap. Consider the view from across the room as well as the practical performance at the window.

How to measure windows for blinds in a recess

For a recess-fitted blind, measure the width in three places: across the top, centre and bottom of the opening. Record the narrowest measurement. Next, measure the drop at the left, centre and right, then use the shortest figure.

This approach allows for the natural variation found in plasterwork, tiles and timber-lined openings. Do not make deductions yourself unless you have been specifically instructed to do so. Made-to-measure blind specifications commonly allow the correct clearance for smooth operation, and an unnecessary deduction can create distracting gaps.

Depth matters just as much as width and drop. Measure from the front edge of the recess to the glass, taking account of handles, trickle vents, tiles and any protruding catches. Venetian, roller, Roman and vertical blinds each require different amounts of space, while layered window treatments require more generous depth.

If you are considering a Roman blind, remember that the fabric stack will gather at the top when raised. A compact recess can still suit a Roman blind, but the finished heading and the amount of daylight it obscures when open should be part of the decision. In a room where every inch of light matters, a roller blind or slim Venetian may be the more practical choice.

Check for obstructions before ordering

Open the window fully and look closely at the surrounding space. Handles that project into the recess, inward-opening casements, alarm sensors and deep window boards can all affect the position of the blind.

It is also worth checking whether the recess is square. Measure each diagonal from corner to corner. A notable difference does not mean you cannot fit a blind, but it may influence whether an outside fit gives the more polished result.

Measuring for an outside-fitted blind

For an outside fit, you are measuring the finished area you would like the blind to cover, rather than the opening itself. Measure the width and drop across that intended area. This is the size you provide, without deductions.

As a general guide, allow an overlap of around 50mm to 100mm on each side of the recess where wall space permits. The ideal amount depends on the blind style, window proportions and your desired level of privacy and light reduction. Bedrooms often benefit from a more generous overlap, while a narrow wall between neighbouring windows may call for a more restrained treatment.

Above the window, allow enough room for the blind mechanism and for the blind to sit clear of the recess when raised. For roller and Roman blinds, positioning the fitting higher can create a more elongated, luxurious impression and reveal more of the glass during the day. Measure down to where you want the blind to finish, whether that is at the sill, below it or to the floor.

When measuring the width, think about the bracket position as well as the cloth or slats. A control chain, cassette or mechanism may extend beyond the main blind, particularly on compact walls or near a corner. Careful planning prevents a beautiful blind from feeling squeezed into place.

Measuring different blind styles

The same disciplined method applies to every blind, but the design itself changes what you need to consider.

Roller blinds are sleek and versatile, with options ranging from softly filtered light to room-darkening fabrics. Check the roll direction and the position of the bracket, especially when window handles sit close to the glass. A reverse roll can sometimes offer improved clearance.

Venetian blinds bring texture and adjustable light control to a room. Measure the recess depth carefully, as slat size affects how comfortably the blind will sit and how much space it occupies when raised. Wider slats offer a bolder, more tailored look, but need more room than slimmer alternatives.

Roman blinds introduce warmth, fabric and softness. Their measurements should be considered alongside curtain poles, pelmets or nearby furniture, ensuring the fabric folds do not interrupt a radiator, window seat or opening sash. The finished effect is particularly elegant when the blind fabric complements cushions, upholstery or a statement wall colour.

Vertical blinds remain a sensible choice for wide windows and patio doors, where practical coverage and easy access are essential. Measure the full area to be covered and decide whether the stack of louvres should sit to the left, right or split in the centre. That detail matters when a door is used frequently.

Bay windows need a more considered approach

Bay windows should never be treated as one broad, flat opening. Each section requires its own careful measurement, and the angles between the windows must be allowed for so blinds can operate without knocking together.

For a square or angled bay, measure the width and drop of every individual window. Note the depth of each recess and the distance from the glass to the front edge. For curved bays, bespoke advice is especially valuable, as the relationship between the individual blind brackets determines whether the finished arrangement feels harmonious.

The same applies where shutters, curtains and blinds may be layered. A beautifully furnished bay can be a focal point of the home, but it needs room for every element to open and stack gracefully.

Avoid the small errors that spoil a tailored finish

Use a steel tape measure rather than a fabric tape, which can stretch or bow. Record figures in millimetres, not centimetres, and measure twice before submitting an order. Label each window clearly if you are measuring several rooms, particularly when the sizes are similar.

Do not rely on the measurement of an old blind. Its brackets may have been positioned differently, the previous treatment may have been outside the recess, or the window may have changed during redecoration. Measure the actual window and the intended fitting position every time.

Finally, consider the room as a whole. A blind is not simply a practical covering. Its scale, colour, texture and position influence how tall the ceiling feels, how daylight moves through the space and how confidently the scheme comes together. For intricate bays, unusually shaped windows or a layered luxury look, a professional measuring service provides welcome certainty. Harvey Bruce Blinds, Shutters & Interiors can help homeowners across Edinburgh and the Lothians bring those details together with precision and style.

The best measurements leave nothing to chance, allowing the finished blind to look as though it was always meant to be there.