In Jainism, “purva” usually refers to a previous birth (a past life). There isn’t a fixed number of years for a purva. The duration of a past life isn’t stated as a universal year count; it varies, and Jain scriptures focus more on the karmic quality of the life rather than a specific age.

If you meant something else by “one purva” (for example, a specific unit or term used in a particular text), please clarify which text or context you have in mind.