What's a healthy length for a guinea pig's nails?

I can't tell if my guinea pig's toenails are too long, do you have an exact measurement or a picture of a healthy length? Thanks!What's a healthy length for a guinea pig's nails?
The longest it should get is about 1.cm, but a lot of people have theirs longer, but that is the healthy length for you and your guinea pigs. My Guinea Pigs is exactly 1 cm, and if they got any longer, every time you hold them, you would get Badly scratched. Your Guinea pigs nails should not be long because if they itch themselves they will cut themselves, and they know when their nails are getting too long, so if they try to chew them off themselves, nails are not a good thing to eat.