Hopefully now you have decided on what type of curtain or blind you want.

It is best to use a steel tape for measuring.

A few pointers before we start
Its best to get a track or pole that is around 15 to 20cm wider than the window on each side (if the wall allows) so you have room for the stack of the curtain so its not blocking too much of your window.

The return of the curtain
do you need to take the curtain back to the wall, so not having a gap between the wall and the track or pole?

Have you had your carpet fitted?
Allow for the depth of the carpet or rug.

How wide should they be?
Firstly decide on the width of the curtain.

A pole: for the curtain to hang from a pole I would need the measurement of the length of the pole not including the finIals, (fancy stoppers at the ends). If the pole is corded let me know as there in normally a crossover in the middle of the pole (so the curtains overlap slightly when shut) as I would have to allow for this.

A track: for the curtain to hang from a track I would need the measurement of the length of the track from end to end, if there is a cross over on the track (an extended arm on one of the runners) so the curtain overlaps when shut.

Then add on the return if needed.

How long should they be?
Secondly decide on the length of the curtain

There are normally 4 options: to the sill, radiator, floor, and pooling on floor.

For French pleat, goblets and pencil pleat headings on a pole I would need the measurement taken from the bottom of the ring where the hook eyes is screwed in, to the length required.

For eyelets I would need the measurement taken from the top of the pole (do not allow for rise above pole as I will work this out) to the length required.

For pooling allow around 15cm of curtain on the floor, please be aware the curtain puddle will have be arranged each time the curtain is opened and closed, or they can look messy. Also the curtains take up a lot more room on the floor and need space so they are not knocked out of the dressed state.