Not all pint glasses are created equal.
In Ireland and Great Britain the internal volume of so-called "pint glasses" is regulated by state authorities in accordance with the imperial system of measure. As such, a state sanctioned pint glass (indicated by an official mark etched on each glass: a crown in the U.K., a circle bisected by a wavy line in the Republic of Ireland, or, in accordance with recent standards set to unify the mark throughout the European Union, the letters “CE” *) must hold a minimum of 20 imperial fluid ounces (the equivalent of about 19 US fluid ounces, or about 1.2 US pints), but the glasses are generally designed with slightly larger capacities than the minimum, ensuring plenty of room for a full imperial pint of beer topped off with an ample head of foam.
European Vs. American Pint Glass Styles
These tall glasses generally come in one of two styles: one with a slight bulge about an inch or so below the rim ("nonic" style), the other with a gentle curvature that begins about 1/3 of the way up from the bottom of the glass, curving in around the rim ("tulip" style). Both styles facilitate a firm grip, provide a wide mouth for easy sipping, preclude locking when glasses are stacked together, and slightly retard and control the escape of the aromas of hops and other volatiles with their inward curvatures.
In the States, where our pint differs in overall volume from the imperial pint and there is no official standard dictating the volume of a "pint" of beer, the considerably smaller, conical pint glass reigns. Filled to the very brim these glasses just barely hold a full US pint (or 16 US fluid ounces), such that, by the time a bit of room is left for some head and for spill-free transport, your pint of beer may be 2 to 4 ounces shorter still—all told, about 1/3 less liquid overall than the average imperial pint.
When stacked, the glasses have a greater tendency than their European counterparts to lock together, and their straight, outward sloping sides do nothing to foster a beer’s flavor enhancing aromas. Though it may be easy to assume that these glasses were put into service by unscrupulous proprietors looking to cheat their patrons out of a few ounces of brew, the full explanation is likely less insidious.
The Origins of the American "Pint" Glass
More accurately called shaker or mixing glasses, these vessels were not originally intended for serving beer at all, but for preparing cocktails and mixed drinks. (To this end, in the 1940s and 1950s these glasses were commonly printed with recipes and markings for making the quintessential cocktails of that age.) As such, they have long been a common find behind the American bar, but it is only within the last few decades that these glasses have become so popular for actual service.
I suspect that as beer tastes expanded in this country and bars began to offer more extensive and international selections, including brews typically served by the pint in their countries of origin, bar owners turned to the largest and most pint-like glasses they had on hand (though some bars pride themselves on serving the "Imperial pint"). The glasses were readily available, durable and inexpensive. Patrons accepted their usage, and before long, American breweries—the contents of whose standard 12-ounce (US) cans and bottles fit tidily within the glasses' confines—began to brand shaker glasses, legitimizing their use as beer serving vessels.
Though I admit to enjoying pints of all sizes, shapes and nationalities, for St. Patrick's Day, I prefer them large, curvy and Irish.