A bar near my house recently started selling "pints" in 16 oz. glasses. What should you be getting in Ontario when you order a "pint"?

According to the Weights and Measures Act:

7. No person shall, in trade, use or provide for the use of a unit of measurement unless
  (a) that unit of measurement is set out and defined in Schedule I or II; or
  (b) the use of that unit of measurement is authorized by the regulations

33. (1) Every person who sells or offers for sale any commodity, by number or unit of measurement, is guilty of an offence if the quantity of the commodity that that person delivers or offers for sale is, subject to prescribed limits of error, less than the quantity that that person
  (a) purports to sell or offer for sale; or
  (b) should deliver or offer for sale on the basis of
   (i) the total price paid or to be paid for the commodity, and
   (ii) the stated price per number or unit of measurement.

Schedule II of the Weights and Measures Act defines a "pint" in Canada as 1/8 of a gallon and a gallon as "454 609/100 000 000 cubic metre". Schedule I defines a litre as "1/1 000 cubic metre". Putting these definitions together, a Canadian pint is, in litres:

1 Pint = 1/8 Gallon x (1 Gallon / 454 609/100 000 000 cubic metre) x (1 Litre x 1/1 000 cubic metre) = 0.5683 litres

The regulations under the Weights and Measures Act allow for a margin of error for pints of 1/4 of a "fluid ounce" (1/160 galloon, or in litres, 0.0284L [28.4mL]). So a pint poured at a bar can't be less than 0.54 litres (540mL). Industry Canada tells consumers that a pint of beer is 568 mL and "the foam (head) is not included in the measurement".

A (rather unscientific) Toronto Star investigation last year found that only 3 of 15 bars they inspected were selling full pints of beer. One beer blogger recently wrote about the trend of bars dropping the word "pint" from their menus in order to keep selling what would otherwise be illegally small glasses of beer.

Federal regulation isn't the only source of beer law in Canada.

In Ontario the Liquor License Act imposes a requirement that bars provide customers with the size of drinks they serve. Under Regulation 719, Licenses to Sell Liquor bars must, as a condition of their license, "make available to, or shall post in locations visible to, persons on the premises lists describing ... (b) the amount of liquor in each type of drink offered for sale;" (the term "liquor" includes beer).

Section 14(1) of the Consumer Protection Act, 2002 prohibits "mak[ing] a false, misleading or deceptive representation". Although a person's remedy might be limited to the amount of beer they didn't get by s. 18(2): "the amount by which the consumer's payment under the agreement exceeds the value that the goods or services have to the consumer".

Industry Canada can hand out multi-thousand dollar fines but consumers don't have much in the way of private recourse. You can file a complaint online with Measurements Canada and send an email to the AGCO. Or could politely raise the issue with a manager: my local bar gave me the beer for free.