In Storey's Guide to Raising Turkeys, there is a table on page 58 titled "Growth rates and feed consumption for (BBW) turkeys" Age increases in two-week increments. According to this table, it will take about 17 pounds of feed to get a BBW tom from 16 to 18 weeks, and 13 pounds of feed to get a hen from 16 to 18 weeks. This works out to about 1 lb of feed per bird per day.
There is another column labelled "feed per pound of live weight." According to the table, a 16 week tom weighs 26 lb, and the feed requirement is 2.4 lb of feed per pound of live weight. 2.3 times 26 is about 62 lbs. Divide this by 14 days, and you get 4.5 pounds of feed per day per tom. The equivalent for hens works out to 3.1 lb per bird per day. So a mixed flock would be about 3.8 lb of feed per bird per day.
So which column do you believe? My free rangning heritage birds are going through the feed at less than half the described rate. But then again, they are free ranging and heritage birds so the comparison has some problems.
How much are they eating?