Candidly, more than you'll ever need. Although an exact number can't be provided, it's 'a lot'. ;-)
Simply, you're more likely to get tired of the effect prior to needing a refill.
So, if this is 'all ya got' for walk around, you'll get plenty of usage out of it, but, if you're doing it with other effects as an act of some sort, it'll last darn near forever.