Hello. With appropriate A times, most babies of his age will take two naps of 1-2 hours each and a shorter catnap. In my opinion (and that of many sleep researchers) a nap shorter than an hour isn't really as restorative, so you want to aim for at least an hour for the first two naps of the day. Whether or not to aim for longer than one hour depends on whether it's long enough for him--does he wake happy? Is he generally happy during the day? Is he sleeping well at night? All of these factors will help you decide whether he's napping enough.
For my baby, I've discovered that she needs between 1 hr 15 and 1 hr 45. If she wakes before 1 hr 15 I will generally try and extend or adjust A times for the next nap.
HTH!