Am I measuring for curtains correctly?

[Madmog]

Width - window is 200cm wide, curtain pole above 215cm. Do I give a measurement of 215cm? If I'm buying pencil pleat, some sites seem to be saying you get two curtains of 215cm to allow for gathering. Does that make sense?

Length - want something around 145cm. When I give this measurement will it include the 3" pencil pleat header?

Typically for pencil pleat and other gathered curtains you need double to width of ungathered curtain for the space you want it to fill/cover. If you are on a tight budget, you could do 1 1/2 times, but it may look as though you've skimped.

The length is the complete length of the curtain including the header tape.

A decent website should have diagrams of different windows/window dressings and guidance of what and how to measure. Some sites will ask just for the window measurements and your preferred length and they'll double the width for making up the curtains. Read the guidance carefully.

If you are unsure then rather than make what could be an expensive mistake, try somewhere like Dunelm Mill and take your measurements in - also measure the window width and height in addition to what is already there - and they can advise what you need. You can get a quote and decide whether to proceed.