How to Measure Blinds for a Square Bay Window

 Square Bay Window Blinds Bay windows are a wonderful feature in a home, often being used as a selling point by letting and estate agents to convince prospective buyers and tenants to move in to a property. However, like any window, a bay window needs the perfect dressing to ensure privacy, light control and to help maintain or improve the look of a room. To ensure your chosen blinds fit perfectly into your bay window, it’s important that you know how to measure the space appropriately. Here, the team at Kingston Blinds will tell you how it’s done.


– Pencil

– Metal tape measure

– Ruler

– 2 pieces of A4 or A5 paper or card


Choose your blind

Different types of blinds have different measurements, so be sure to know which blind you’re having and its dimensions. For roller blinds, remember that the cloth of the blind is slightly narrower than the bracket to bracket measurement, so it won’t be able to fully cover your window unless there’s large window framework in place.


Roller blinds

You must also choose whether or not you will opt for a top or face fixing with your blind. If you are going for the face fixing, you must take the following allowances into account to cater for the depth of the headrail:

Blind under 200cm wide: 60mm rail depth

Blind over 200cm wide: 80mm rail depth

For top fixings, the allowances are:

Under 200cm wide: 50mm rail depth

Over 200cm wide: 70mm rail depth


Wooden blinds

When using wooden blinds, you must take into account the size of the wooden slats, as this directly affects the required rail depth. The allowances are as follows:

25mm slat: 55mm rail depth

35mm slat: 65mm rail depth

50mm slat: 70mm rail depth

63/64mm slat: 80mm rail depth


Vertical blinds

Your measurements must be adjusted accordingly when applying vertical blinds to a bay window. For example:

Vertical blind 89mm slats: 70mm rail depth

Let’s go through the overall process of measuring your windows for your new blinds.

Step 1

Measure the total width of the front bay window, which is usually the largest window in the bay. These measurements should be carried out to the nearest millimetre, and this will be the measurement used when you order your new blind.

Step 2

If there are handles on your bay window, measure how much they protrude, as this can impact the way your blind fits into your square window. We’ve used a handle as an example, but if there’s any sort of obstruction on the window frame, make sure to measure its protrusion.

Step 3

Combine the depth of your blind and the aforementioned measurement of your handles or obstruction, and measure the combined distance away from the main window.

Step 4

From the point where you measured the aforementioned ‘combined distance’ in step 3, mark where you’d like the blind to finish. This will be the width of your ‘return’ blind.

Step 5

Measure the length of your window. Do this three times to make sure you achieve the most accurate measurement possible. Of the three measurements, note the smallest one, as this will be given as the ‘drop’ when you order your blinds.

Step 6

Time to order your blinds. Give the professionals at Kingston Blinds a call and let’s arrange the delivery and installation of the perfect blinds for your room.


Kingston Blinds are experts in the design, delivery and installation of the perfect blind for your square bay window. For more information, please get in touch with us today on 01482 407 319 or use our handy contact form and we’ll be more than happy to help.

  • We manufacturer our own high quality blinds
  • Free quotations & home visits
  • All work fully guaranteed
  • Reliable staff
  • Made-to-measure service

Get a free home visit from one of our team.

Call us today on
01482 407 319.