Once again, my non-beer-drinker status has collided with my professional responsibilities. In this translation, I need to find an English term for a “galopin,” which is apparently a beer glass holding 140 ml or about 5 fluid ounces. Help?
In English, we would call that a “damn small beer!” That must be the size they use in casinos for the drinks you get at the tables.
“a small glass of beer”
Googling “galopin” and “beer” leads to a number of definitions, none of which use any special terms for an equivalent drink size in English.
In this case, it’s the size of glass used on a wheel offering samples of eight different microbrews.
I’d always gotten bottles at the tables. But, I get those small glasses when actually paying in the restaurant.
Then I’d refer to it as a “sampler” glass. Any pub offering such an item would know what you mean.
And in England, we would call it an illegally small beer 
(third-pint glasses being the smallest permissible measure)
I was gonna suggest dram but I’ve never heard that used with anything but whiskey.
According to this Google Answers, that there be a pony. Oh, based on the 140ml measurement. Otherwise a French galopin varies in its measurement.
I thought a pony was 1.5oz.
It’s only a pony if you’re talking to some bartender DownUnder. Up here in the right hemisphere, a pony as a drink measurment of 1 ounce. An ounce and a half is a jigger.