When it comes to purchasing a ready made roller blind, they are usually been designed for standard window sizes. However, there really is no such things as a standard window, as homes across the UK have been built to different specifications, by different people and at different time periods.
So unless you are really lucky you will need to buy a roller blind that is slightly larger than your window, and then make adjustments. Doing this is relatively easy, so if you want save a little bit of money then this can be a great option. However, if you aren't that handy and know for a fact you will ruin the overall finish of the blind then you might want to opt for the made to measure option. Let's go through the process of adjusting a roller blind and then you can decide what is right for you:
Firstly, you will need to measure the width inside your window frame. It's best to measure the width at the top of the window, although you might want to take width measurements at several different heights in case your window is wonky. Should the blind be going into the recess of the window it is best practice to take 1cm off your measurements for the perfect fit, and you should also take into consideration the space required for brackets.
Now that you know how much space you have to play with you can start to apply these sizes to your roller blind and mark your blind fabric with light pencil marks, at the distance at which you want to cut the blind. To do this it is best to completely unravel the blind fabric and place it on a flat surface. It is much easier to adjust the blind like this as otherwise you may make uneven or sloping cuts along the fabric, and make the blind completely dishevelled.
Note: You must trim the blind on the side that doesn't contain the cord. The head rail will need to be trimmed too using a hacksaw, so if you trim the corded side of the fabric then you would have to saw off the controlling mechanisms too - which would make the blind inoperable. Place the unrolled blind on a flat and square surface, such as a dining table. Align one edge of the fabric with the edge of the table, by doing this you will have a solid edge that will not move or fold under tension.
Using the edge of the table to hold your tape measure, you can now extend the measure across the width of the blind and make a pencil mark at the distance at which you want to cut the blind. When doing this ensure the tape measure is parallel to the top or bottom of the table, this will make the line square. Repeat this process at multiple points along the height of the fabric. You will now have a dotted line. Join the dots using a straight edge or long ruler, marking a line along the fabric with a pencil.
Cutting your blind fabric
If your blind is made using PVC or a similar material then you may be able to cut the fabric using a craft knife. If you do so you will want to insert a cardboard sheet under the fabric to ensure you don't damage your table. For thicker materials you may want to use a sharp pair of fabric scissors. When you are ready and happy with all the measurements and guidelines you have drawn then go ahead and cut your fabric.
Trimming top and bottom rails
You should now be left with a bottom rail and top header mechanism that are both too long on one side, and blind fabric that is cut to the required width with a neat edge. It is now a matter of sawing through these protruding rails both at the top and bottom of the blind. Saw slowly through each rail, so as not to crush or disform the plastic or sometimes cardboard components.
Once you have done this you will have two loose pieces, which will contained end caps, these can be removed by hand and placed back onto the recently cut bottom rail and top header mechanism. You can then discard the surplus pieces of rail. You should now be left with an adjusted roller blind that is narrow enough to fit within your window. If you have taken your time and followed these instructions carefully then all cuts should be smooth, straight and the blind will look as if it was made to measure.