Men's Health states that, as of 2014, the average bicep size in men when not flexing is around 13 1/2 inches. Stack Me Up rates the average flexed bicep size between 14 1/2 to 15 inches.
Stack Me Up offers a bicep size chart that ranks a user's results against other men or women in the United States. First, the user enters the measurement of his or her flexed bicep in inches. Next, he or she selects the gender and whether the results should be filtered by age.
To get bigger biceps, Men's Health recommends a variety of exercises, including isometric chin-ups and dumbbell curls.