Well, I agree that the question is vague, but I suspect you are asking about the battery or the actual 'lifespan' of the device? For the first question, the usual answer for a fully charged iPad battery is about 8-10 hrs, but many factors may affect & reduce that time - check Apple support or Look HERE for some suggestions on how to prolong the battery life on the iPad3.
Now for the actual lifespan of the device, I would guess until you want a new model or until you break the one you own!
If these comments do not answer your question, then be more specific - good luck!