A bay window should feel like an architectural feature, not a measuring challenge. To measure bay windows accurately, you need to work with each individual window face while also considering the complete look: where treatments will meet, how they will stack, and how much natural light you want to retain. A few millimetres can determine whether a made-to-measure blind sits beautifully within its space or catches on the neighbouring window.

For homeowners investing in bespoke blinds, curtains or plantation shutters, careful measuring is the first step towards a finish that feels crafted with precision and style. Use this guide to understand what to record before arranging your chosen window furnishing.

First, decide how your bay window will be dressed

There is no single correct way to dress a bay. The best approach depends on the window’s shape, the depth of its recesses, the room’s use and the level of privacy or light control required.

Individual blinds are often fitted to each window section. This creates a clean, tailored appearance and makes it easy to adjust light across the bay during the day. Plantation shutters can be designed in a similar way, with panels following the angles of the window for a timeless architectural finish.

Curtains, meanwhile, may sit on a shaped track or pole across the full bay, or be paired with blinds for a more layered, luxurious scheme. A full-width curtain treatment needs allowance for stacking at either side, so it should never be measured in exactly the same way as three separate blinds.

Before reaching for the tape measure, decide whether you are measuring for a recess fit, an outside-recess fit, shutters, or curtains. Your measurements must suit the treatment, rather than simply describe the glass.

What you will need before you measure

A rigid steel tape measure is essential. Fabric tapes can bend around corners and introduce small inaccuracies that become much more obvious once a bespoke product is installed. Keep a pencil, paper and a phone camera to hand, too. Photographs of the bay, including the ceiling line, sill and any handles, are remarkably useful when discussing your requirements with a specialist.

Record all figures in millimetres. Write down the width first and then the drop, for example 865 mm x 1,240 mm, and clearly label each section as left, centre or right when facing the window from inside the room. Never rely on memory or assume that matching-looking windows are identical.

Pay attention to anything that projects into the space: handles, trickle vents, tiled reveals, radiators, deep sills and alarm sensors can all influence the final specification.

How to measure bay windows accurately for individual blinds

Most angled bays have three faces: a wider central window with two narrower side windows. Treat these as three distinct windows, even when they share one continuous sill.

Measure the width of every recess

For a recess-fitting blind, measure the internal width of each window recess in three places: at the top, middle and bottom. Take the smallest figure. Old properties, including many elegant homes across Edinburgh and the Lothians, do not always have perfectly square reveals. Using the smallest measurement helps prevent a blind from rubbing or failing to lower smoothly.

Measure from the inside edge of one recess wall to the inside edge of the other. Do not measure the glass alone, and do not include the angled plaster return that leads into the adjacent section. Each blind needs its own clear, usable width.

For an outside-recess fit, measure the area you want the blind to cover rather than the recess itself. Allow enough overlap on both sides to reduce light gaps, while checking that the blind will not interfere with a neighbouring treatment. The required overlap varies by blind style and available wall space, so it is sensible not to add arbitrary allowances until you know the product being fitted.

Measure the drop in three places

Take the drop from the top of the recess to the sill at the left, centre and right of each window face. Again, use the smallest measurement for a recess fit. This matters where a sill slopes slightly or has been fitted unevenly.

If you would like the blind to finish above the sill, measure to the exact point where you want its lower edge to sit. For a blind that will extend below the recess, record the intended finished drop and check for obstructions such as a radiator or window handle.

Check the meeting points between blinds

This is the detail often missed in a DIY measurement. Where the side and centre blinds meet at the bay corners, their headrails, brackets or fabrics need enough clearance to operate without collision. The closer the angle, the more carefully this must be assessed.

Do not assume three blinds can occupy the full width of their respective recesses if their fittings meet at a tight internal corner. Depending on the blind type, modest deductions may be needed so the treatments sit comfortably alongside one another. Roller, Venetian, vertical and Roman blinds all have different hardware dimensions.

For this reason, record the bay angles as well as the widths. Place two straight edges along the faces of adjoining windows and photograph the corner from above if possible. A professional survey will confirm the final deductions, but good notes allow for a far more productive initial conversation.

Measuring a bay for curtains and Roman blinds

Curtains bring softness and generous texture to a bay, particularly in bedrooms, drawing rooms and dining spaces. They are also the option where a shaped pole or track can make the overall composition feel especially considered.

Measure the intended track or pole position, not merely the window width. For a full bay track, start at one end point and follow the route across every angle to the opposite end point. A flexible tape can help establish an approximate route, but the finished track should be surveyed or templated by a professional, especially for sharp or irregular angles.

The height should be measured from the proposed top of the track or pole to the desired curtain finish. Consider whether curtains will skim above the floor, kiss it lightly or form a more formal puddle. In a bay with a projecting sill, curtains commonly finish just above the sill or are positioned to clear it elegantly.

Roman blinds generally need the same width and drop information as other individual blinds, but their folded stack deserves extra thought. When raised, a Roman blind occupies a portion of the upper window. Check that it will not obscure too much glass, clash with opening sashes or conceal a beautiful feature such as a stained-glass fanlight.

Why shutters call for a professional survey

Plantation shutters are engineered to the exact contours of the window, making them exceptionally rewarding in a bay but less forgiving of rough measurements. Frames, panel configurations, louvre clearances and bay posts must all work together. Even a slight error in angle can create uneven gaps or affect how the panels open.

You can take preliminary dimensions to explore styles and budgets, but final shutter measurements should be confirmed through a specialist survey. This is particularly valuable for bays with curved sections, uneven walls, shallow recesses or outward-opening casement windows. Basswood shutters are a refined, durable choice, and their finished appearance relies on the accuracy of the framework as much as the beauty of the material.

At Harvey Bruce Blinds, Shutters & Interiors, a measured consultation helps translate those practical details into a considered scheme that complements the wider room, from wall colour and flooring to furnishings and lighting.

Avoid these common bay window measuring mistakes

The most frequent error is measuring the glass rather than the space where the treatment will sit. Another is using one overall bay width for individual blinds, which tells you little about the clearance required at each corner. It is also easy to overlook handles and opening windows until the new treatment arrives.

Avoid rounding numbers up or down. Record the exact millimetre figure, measure twice, and compare the second reading with the first before placing an order. If the measurements differ, investigate why rather than choosing the figure that seems more convenient.

Finally, do not make deductions for a recess-fit product unless the supplier specifically instructs you to do so. Many made-to-measure services apply their own fitting tolerance. Deducting twice can leave unwanted light gaps and spoil the tailored effect you were hoping to achieve.

When a home measure is enough, and when to ask for help

A straightforward square bay with three generous recesses may be suitable for careful home measuring, particularly when choosing individual blinds. Yet a professional measure is worth considering whenever the bay is angular, curved, shallow, uneven or intended for shutters and shaped curtains.

It is also the more reassuring choice when the room is a key entertaining space or a principal bedroom, where window treatments will shape the atmosphere every day. The right measurements do more than ensure a good fit. They allow the finished blind, curtain or shutter to frame the light beautifully, preserve the proportions of the bay and give the room the calm, elevated character it deserves.