The average cow size across all breeds was 1,390 lbs., with less than 100 lbs. separating the heaviest and lightest breeds. Herefords came in heaviest, at 1,419 lbs., followed by Angus at 1,410 lbs., then Red Angus at 1,409 lbs.or the Angus breed, yearling weight, which is considered a reliable indicator of mature weight, has increased 96 lbs. since the early 1970s. In that same time period, Angus steer weights have increased 300 lbs., and heifers are up 239 lbs., on average.