Help! Measuring curtains (added fun it's for a static caravan)

[OllieCollieWoo]

My head is going to explode. I can't figure out the size to buy.

I'm tasked with replacing curtains for a static caravan.
Doing the bedroom.
I can't measure the caravan (I'm not there) but kindly been given existing curtains. Measured them;

So 1st question:
Are curtains measured on curtain material size or window size?

2nd Question
Anyone know any good caravan curtain companies ?

So if you were buying bespoke you'd measure the window. For short curtains you'd want 2-3x the width of the window plus hemming and from the height of your curtain rail to 5-10cm below plus pattern repeat plus hems, all per drop.

I love you @JaninaDuszejko