The average size of a tuna fish ranges between around 15 inches to about 79 inches. The average weight varies greatly, from as small as 3 pounds to as large as 400 pounds.
The average size of a tuna fish depends upon the species of the tuna fish. An albacore tuna fish averages around 15 to 40 inches in length and has a weight of approximately 10 to 25 pounds. The Atlantic or northern bluefin tuna, one of the largest species, weighs around 550 pounds.
Other species of tuna include the southern bluefin, bigeye, bonito, skipjack, tongol and yellowfin tuna. The skipjack tuna is the most commonly consumed tuna. It has an average size of around 15 to 30 inches. Skipjack tuna fish make up around 70 percent of the world's canned or pouched tuna.