16 oz would last me a month, if I condition twice a week. Even when I didn't have a clue about adding conditioner till my hair got seaweedy, and I still used to finish my 8oz in a month. If I can avoid it, I would not use a conditioning conditioner to co-wash as well; that way I can stretch it out a little longer.

I did finish one Suave Naturals conditioner in less than a week, but I was swimming a lot and using it as a pre-swim conditioner, co-wash, regular condish, and leave in.