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How To Measure For Window Blinds

Standard Windows

Measuring for Window Blinds: The Definitive Guide

Blinds Direct is the best place to shop online for custom window blinds, but it can be difficult to know where to start when you’re making your selection. Luckily, we’ve put together this handy guide that will walk you through the measuring process so you can be sure you get precisely what you want in your new window treatments!

Recess Size - Inside Window Recess

If the blind is meant to be inside the window recess, this is a measurement you need to make. Give us the measurement of the width and the height from three different positions so we can provide you with the shortest length. If it becomes necessary, we will make necessary deductions to ensure the blind can fit into the recess of the window.

Roller Blinds

Please note that the width of the fabric you receive will be 3-4cm narrower than the actual recess size.

Blackout Blinds

You may have better results when installing a blackout blind when the opening of the blind is inside the window, measuring to the width of the recess, rather than on the outside of the window opening.

Vertical Blinds

With this type of blind, the headrail is included in the top edge of the blind, meaning the louvres will be shorter than the edge.

Exact Size - Outside Window Recess

Also known as pin width or finished blind width, an exact size blind is a measurement you'll need to make if the blind needs to hang outside the recess overlapping the window. There should be at least 7.5cm of overlap at each side and the top and bottom so as to keep as much external light out as possible. Get three different measurements for the width and height, the smallest of which we will keep. The most important thing is to keep providing us with more measurements.

Roller Blinds

Please be aware that this is the total width of the blind and does not include the width of the blind mechanism.

Vertical Blinds

The headrail is included in the fall of the blind and so the louvres will be shorter than the fall.

French Doors

Recess Size - Inside Window Recess

If the blind needs to be installed inside the recess, this is the measurement you need to take: the distance from one wall to the other and then the drop from the top of the recess to the floor. Please take this measurement three times, always remembering to provide the smallest measurement. If needed, we will subtract certain areas of the fabric so that the blind will fit into the recess.
Please be aware that your chosen blind might not work on your door if your door swings in (for example).

Exact Size - Outside Window Recess

The exact size blind needed is also known as pin width or finished blind width. You will need this measurement if the blind needs to hang outside the window frame and overlap the door. Determine how much overlap you want on each side, we recommend at least 7.5 cm. Leave this same amount on the top so you reduce external light to a minimum.

Measure the width and the drop in three different positions and ensure that you provide us with the smallest measurement. No deductions will be made from the measurements provided.

Don't forget to check if the kind of blind you want to buy is compatible with the kind of door you have (such as an inward-opening door).

Angled Bay Window


Before you start measuring, select the correct headrail depth from the table on the right. Please measure any window handles or vents that protrude out of the window frame and add this to the head rail depth.

This will be the basis for Step 1 below.


Cut two pieces of cardboard to measure 300mm x 300mm, taking into account the handle that sticks out of the window.

An example would be, if you need 35mm slats and need to account for a 30mm protruding handle, then use a depth of 90mm (60mm + 30mm).


Gently slide two pieces of paper towards each other across the top of the window's sill.


Draw a small line with a pencil on the outside edge of the window on the line where the paper meets the frame. You will need to repeat the two preceding steps for each corner of your bay window.


Record the spacing between the horizontal and vertical slats that you have drawn, this will determine the size of the blinds you will need to order.


Set the height of the blind, measuring from the top of the blind to the point where you want it to stop - usually on the window sill.

Boxed Bay Window


Look for the rail depth of your chosen blind on our helpful table. Write it down before you start measuring. Pick a certain style and, once you know the dimensions of your bay windows, follow the directions of your choice.

If the edges of your blinds are going to come up against a wall, take 5mm off the overall length.

Option 1

Here, the front blind fills the window entirely and the side blinds go against the front blind. Measure the full width of the bay then subtract 15mm and order for exact fitting. First, measure the width of each side blind, making sure to measure in the same way, and then subtract the rail depth to find the accurate measurements. Place the order for your side blinds as exact fitting.

Handles, openers and vents
If you have any obstructions on the window, measure how far they stick out past the window.

Option 2

To ensure this is compatible with your window, you should measure the size of your window frame: the space from the corner of the bay to the start of the glass frame in the window. Make sure any of these measurements are bigger than the rail depth of your blind, or the blinds will not cover the glass and there will be gaps. In this case, we recommend considering a different option.
With this style, all three blinds meet in the corner of the bay, never overlapping, so measuring is quite simple, just measure all three sections right in the corners. After calculating the rail depth, deduct half the amount from the measurements for the side blinds and double the amount from the measurements for the front blind. The order all blinds as 'exact fitting' in the end.

Handles, openers and vents
Be aware that objects on the outside of the window frame will affect the width of the blinds. You must deduct this amount from the measurements given for the side blinds.
Objects near the side windows will reduce the width of the front blinds. You need to measure how far the object sticks out from the side window frame, and deduct that measurement from the width of the front blinds.

Option 3

If your side windows are too small for the other options, then this one will be the most suitable for you. This one, in particular, continues the side blinds into the corners, while the front blind sits between them. When measuring each side, take 15mm off. Then measure the back side, take double the depth of the rail, and add that to the back side. Order the longer side of the frame (because it will span both rails) as an exact fit, and the short side as exact fitting.

Handles, openers and vents
If your window obstruction prevents the full opening of the blinds, make a measurement of how far the obstruction reaches from the side window frame, and deduct that from the measurement of the front blinds.

Make sure to double-check that width three times, because the width of a bay window can be misleading. Generally, the smallest of the three measurements will be the one you use.

All three are identical from the point where the blind is being mounted down to the window sill. Remember that the length of the rail includes the length of the drop, so make sure you have at least 50mm (5cm) of space for installation.

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