Curtain measuring help

[Curtainnovice]

Ok so I seem to have forgotten how to measure curtains!
How do I do it? Just had to return a pair which were far to short 😂

Length is easiest to measure, from top of header to wherever you want them to finish, ie. Below windowsill, floor, above radiator. Width depends on the style of header but 1.5 width of window at least.