Do you need glasses if you have 20 30 vision?

Depends: It depends on how well you want to see. It does not hurt your eyes in any way if you do not correct your vision. It is just a matter as to how much the 20/30 vision bothers you, and how important it is to you to see 20/20. If you are happy with your vision, glasses are not necessary.

Probably: If the cause is refractive, then glasses or contact will correct the vision. If it is something else, then you may need some other medical or surgical treatment. See and eye doctor.