How to Measure Window Blinds for a Perfect Fit

A blind that is a few millimetres too wide can catch on the recess, while one that is too narrow lets in unwanted light and compromises privacy. Knowing how to measure window blinds properly before ordering is the simplest way to avoid delays, extra cost and a finish that looks less than made to measure.

The right method depends on where the blind will sit. Recess fitting places it inside the window opening for a neat, contained look. Exact fitting, sometimes called face fitting, positions it outside the recess on the wall, window frame or ceiling. Both can look excellent, but they require different measurements.

Before You Measure Window Blinds

Use a metal tape measure rather than a fabric tape. It stays straight across wider windows and gives a more dependable reading. Measure in millimetres, not centimetres, and write every figure down as you go. A steel tape, pencil, paper and a step stool for higher windows are usually all you need.

Do not assume that two windows in the same room are identical. Older properties in particular can have slightly uneven recesses, even where windows appear to match. Measure each window separately and label the dimensions clearly, especially if you are ordering several blinds.

Before choosing the fitting position, look for anything that could affect the blind’s operation. Window handles, trickle vents, tiles, deep sills, alarm sensors and opening doors all matter. A well-measured blind must not only cover the glass - it must open, close and sit neatly in everyday use.

How to Measure Window Blinds for a Recess

A recess fit means the blind is installed within the opening around the window. It is a popular choice for roller, Venetian, vertical, Roman and pleated blinds because it creates a clean appearance and leaves the surrounding wall unobstructed.

Start with the width. Measure the inside width of the recess at the top, middle and bottom. Use the narrowest of these three measurements. This is essential because few recesses are perfectly square, and using the widest point may leave you with a blind that will not fit.

Next, measure the drop in three places: left, centre and right. Use the shortest drop measurement. For the depth, measure from the front edge of the recess to the glass or any obstruction behind it. Depth is particularly relevant for Venetian blinds, roller blind brackets and products with larger headrails.

Give the measurements exactly as taken unless your supplier specifically asks you to make a deduction. A made-to-measure blind supplier will normally allow the correct clearance for the blind to operate within the recess. Reducing the width yourself can create visible side gaps and spoil light control.

Check the Recess for Obstructions

A recess may look straightforward until you spot a protruding handle or a vent near the top of the frame. Check that there is enough unobstructed depth for the blind and its brackets. With roller blinds, consider whether the fabric will roll close to the glass or sit forward of the bracket mechanism.

For tilt-and-turn windows, opening windows and doors, a recess blind may not always be the most practical option. Perfect Fit blinds are often a useful alternative for suitable uPVC windows and doors, as they fit neatly to the frame and move with it. The best choice depends on the frame type, opening direction and how frequently the window is used.

Measuring for Exact-Fit Blinds

Exact-fit blinds are mounted outside the recess. They are ideal where the recess is shallow, uneven or interrupted by handles and vents. They also offer stronger light coverage around the edges, which can be useful in bedrooms, offices and rooms with bright afternoon sun.

For the width, decide how far you want the blind to overlap the recess on each side. Around 50mm to 75mm either side is common where space allows, although narrower overlaps may be necessary beside cupboards, radiators or neighbouring walls. Measure the recess width, then add your chosen overlap to both sides.

For the drop, measure from the position where the top bracket will be fitted to the point where you want the blind to finish. This might be just below the sill, level with the sill, or lower if you want the covering to extend over it. Make sure the proposed bracket position is solid enough for fixing and does not interfere with vents or opening sections of the window.

If fitting above the recess, leave enough room for the headrail or roller mechanism. Roman and vertical blinds often need more clearance than a compact roller blind. For ceiling-mounted blinds, check the ceiling is level and consider whether curtains, coving or nearby doors will affect the available space.

Decide Which Way the Blind Will Roll

For roller blinds, you may be able to select a front roll or back roll. A front roll sends the fabric forward over the tube, helping it clear protruding handles. A back roll keeps the fabric closer to the window and can give a tidier profile where handles are not an issue.

This small decision can make a noticeable difference. If there is a handle, measure how far it projects and discuss the option before the blind is made. It is far easier to choose the right roll direction at the measuring stage than after installation.

Measurements for Common Blind Types

The same recess and exact-fit principles apply across most blind styles, but the product itself can influence the final decision. Venetian blinds need enough depth for their slats and headrail to operate comfortably. Vertical blinds need consideration at the bottom too, particularly above radiators or where doors open into the room.

Roman blinds have a fabric stack when raised, so allow for the space it will occupy at the top of the window. If the window opens inwards, make sure the raised blind will not prevent access. Panel blinds need clear space to stack to one or both sides, while roof lantern blinds and conservatory blinds require measurements that account for the shape, pitch and fixing points of the glazing.

Conservatories are rarely standard. Heat, glare and awkward roof sections can make a simple tape-measure approach unreliable. Bespoke conservatory sail blinds are measured to suit the individual roof layout, providing shade without the bulk or cost often associated with traditional conservatory blind systems. They can reflect up to 70% of heat while remaining easy to remove for seasonal cleaning or storage.

Avoid These Common Measuring Mistakes

The most frequent error is measuring only once. Taking three width and three drop measurements takes a few extra minutes, but it can prevent an expensive ordering mistake. Another is confusing fabric size with the overall blind size. On some roller blind systems, the fabric is narrower than the complete bracket-to-bracket width.

It is also worth checking whether the control chain or cord needs to be on a particular side. Choose the side that is easiest to reach and least likely to be obstructed by furniture. For child safety, controls must be fitted with the appropriate safety device and positioned with care.

Avoid measuring around existing curtains or old blind brackets. Measure the actual recess or the intended new fixing position instead. If you are replacing a blind, its dimensions may not represent the correct size for the window, particularly if it was fitted years ago or made to a different specification.

When a Professional Measure Is the Better Choice

Measuring standard square windows can be straightforward, but some jobs benefit from expert advice. Bay windows, large commercial openings, shaped glazing, bifold doors, roof lanterns and conservatories all need closer attention. The same applies when you want several blinds aligned across one room or need reliable heat and glare control in a workspace.

A professional measure also helps when you are unsure which product suits the space. The right blind is not simply the one that fits the window. It should work around the room, give the required privacy and light control, and stand up to daily use. Blinds and Sails provides free measuring and fitting, helping customers get a made-to-measure result without the uncertainty of ordering from figures taken at home.

Take your time, check every measurement twice and think about how the window is used rather than how it looks when closed. A carefully measured blind turns a practical window covering into a finish that feels properly part of the room.