Because the amount per turkey will vary with the age and size of the turkeys, the environment they're kept in, etc. the best thing to do is take a few days to get a feel for your flock's needs. Fill up your feeders, whatever type you have, and then keep watch over them. Check a couple times per day until the feed in the feeder gets low. Ideally you want the feed to last until the next time you wish to fill up your feeders -- I recommend doing so every or every other day -- but not have so much left over that you risk pests stealing the feed, it going stale or rancid, etc.
Within a very few days you'll know how much your flock requires. Just aim to have a little leftover each night when they've gone to roost -- or if you fill feeders every other day to have a little left over when they go to roost every other day.