In an era of shrinking toilet paper rolls, candy bars, and ice cream containers, something unusual is going on at Costco. They have actually gotten some manufacturers to upsize their tuna cans.
Over the past decade or two, tuna cans have gone from 7 ounces to 6.5 ounces to 6.25 ounces to 6-1/8 ounces to 6 ounces and finally to 5 ounces last year. But look at the new Costco Kirkland brand cans:
*MOUSE PRINT:
They have gone up to 7 ounces, and so have Chicken of the Sea and Starkist brands sold at Costco. The increased size comes at an increased price, no doubt, but tuna cans are now back to their original size. It appears that Costco is the only seller of the new upsized cans.
In Costco’s monthly magazine, their consumer reporter touted the fact their tuna contains fewer fillers and less water than competitors. She went on to say that you get triple the tuna in their 7-ounce can (12 tablespoons) compared to the tuna found in some brands’ 5-ounce cans (4 tablespoons). She enlisted her husband to do the test, as noted in the box on the left.
How is it possible that the 7-ounce can of tuna can contains triple the amount of tuna of a 5-ounce can when it only contains two extra ounces of contents? The answer is it can’t unless the brand name manufacturer is packing more ocean in its cans than tuna.
Our trusty mouse measured the amount of tuna in a 5-ounce can of Chicken of the Sea solid white tuna, first squeezing out the water, and found that it contained one-half cup, which is 8 tablespoons (not the four tablespoons that Costco claimed).
It is reasonable to believe Costco’s claim that its brand of tuna in 7-ounce cans contains 12 tablespoons of tuna (3/4 cup), if a 5-ounce can of other name brands contains 8 tablespoons (1/2 cup). It is not however plausible that Costco’s brand contains triple the amount of tuna. Two requests to Costco to comment on their claim went unresponded to.
Costco’s 7-ounce cans cost $1.50 each (in packs of eight), while sale prices for brand name tuna in 5-ounce cans are typically about a dollar. That makes them just about equivalent.
If a butcher puts his thumb on the scale, you wind up paying for meat you never actually receive. 
