Coilover/Springs - how do you measure them?

[TomTom]

I have some springs but I'm not sure whether thay re 60mm or 40mm - all I want to know is how do you measure them?

[R1CH]

You won't be able to tell what amount they'll lower the car by from measuring them, it all depends on how they've been wound.
You could have 2 sets of springs, 1 -25mm set and 1 -60mm set, the -60mm set could actually be longer, as said its down to how their wound and not just the actual length of the spring.

Edit:
Just read the title again, are these Coilover springs ? what are you wanting to measure, the diameter or how much there gonna lower the car by ?
Coilover springs are normally listed as 1.9" or 2.25" (internal diameter).