Do not take this process lightly. The famous saying “Measure twice, cut once” is famous for a reason. I know it is very simple but that is why it is easy to make a mistake. It is recommended that you use a metal tape measure, not your hard school ruler that you flip until you get to the other side then just skew a little because it is just too long to fit inside the window sill. Trust me I have a degree in math ( I know useless), triangles are deceptive, why do you think popcorn buckets are going from straight-sided to slightly slanted. The difference looks small but the actual change is large.
Simple tips for a Great Fit:
1. Take height and width measurements especially for inside mount from a few different locations, such as top middle and bottom. Your place was built by humans after all, and you don’t want any catching on the side or having a small gap at the bottom of your new blinds.
2. Measure Twice!
3. Use a tape measurer (The last two for those just skimming through)
4. Pay attention to the direction of your roll. Using front roll or the blind exits the farthest away from the window usually for inside mount that way it does not get caught on any lips or handles in the way. Alternatively, there is back roll usually on outside mounts for flushness.
You need to know where you are mounting to know how to measure roller blinds.
Meaning inside your window frame, for this method you need at least a 60mm depth in your frame. After that, all you need is a simple height and width and you are good to go.
For this method width is less important, it needs to be wider than your frame but anywhere past that is your choice. Most importantly you need to make sure your height is right. Being level is also important but if your kitchen floors are not level people are less likely to notice a slightly off-kilter shade mount than that one side of your shade is touching the floor and the other is not.
If you have a valance you need to make sure that the width will be outside the window frame but within the valance width.
If you are linking rollers you can get more specifics on how to measure roller blinds that have been linked. You can expect only to be able to link two together though so it is important to decide which ones you want to be linked if you need more than two, and also consider where you want to drawstring or strings to be located. To help with this consider where you doors or latches are located, and what size each roller is since they can come in different widths. After that, you pretty much follow the same process when measuring for inside or outside mount.
If you do not have the proper tools or experience at installing blinds it is not the most difficult around the house task to take up, but I would still recommend getting someone with the proper experience to do it for you.