The above table is from Paolo Cavallini's paper entitled "Variation in the Body Size of the Red Fox," which was printed in the December 1995 edition of Ann. Zoological Fennici, in Helsinki, Finland.
Dr. Cavallini's paper includes data on the size of red fox from all over the world (Australia, Italy, Jordan, Spain, Switzerland, several states in the USA, several regions within Scotland, several regions within England, the Netherlands, Denmark, Norway, Wales, Ireland, and East Germany).
In all the countries and regions listed, the number of fox measured was greater than 10 for each sex, while 300 were measured in Italy alone. In short, Dr. Cavallini's global data set totals well over 700 weighed fox.
What did Dr. Cavalini discover about fox weight? For one, he found that across the globe the average male (dog) fox weighs just 13.85 pounds, while the average vixen weighs just 11.60 pounds.
The heaviest fox came from a subsection of Scotland where the average adult dog fox weighed 16.09 pounds, while the heaviest average vixen from the same area weighed 13.7 pounds.
Dr. Cavallini provides detailed information about the 300 Italian foxes weighed and measured. The heaviest dog fox in this sample weighed 17.97 pounds, while the lightest vixen weighed 7.16 pounds, and the average fox weight was 12.01 pounds and the average chest size was 14.13 inches for males and 13.27 inches for females.
Dr. Cavallini's research concludes that "body size of the red fox may be variable even within a small area," but also suggests that the average red fox, wherever it is found in the world, is a much smaller animal than commonly believed, and that even in the regions with notably "big" fox, the average fox weighs only between 13.7 and 16 pounds.