From Sociological Images:
In this 1950s ad for soda, the text proudly proclaims that a 12-oz. can is “king-size,” and includes 2 full servings.
Compare it to this sign at Long John Silver’s, where the smallest size is 20 oz., and a 32-oz. medium soda, presented as the default size, is nearly 3 times as large as the 1950s king-size double serving (though, as a reader pointed out and I didn’t think to mention, we do have to make some allowance for ice in the cup).
I quit soda back in March (along with fast food). Smartest decision I’ve made in a long time.