Difficult to answer with any accuracy.
During the drying process meat loses weight as it loses moisture. The amount of weight loss depends entirely on how “wet” or “dry” the Biltong Lover prefers the end product. For those who prefer Biltong so dry that it flakes into dust when breaking it into portions will experience much greater loss of weight than those preferring it “wet and fatty”.
A rule of thumb guestimate is a loss of about 25-35%+.