There are 3 teaspoons in a tablespoon in the US and UK systems. A US tablespoon holds about 14.8 mL (half a US fluid ounce), and US nutrition labels round it to 15 mL, the same as the metric tablespoon used in most countries.
Australia is the main exception: its tablespoon is 20 mL, which equals 4 teaspoons, so recipes from there call for a bit more per spoon.
Source: Wikipedia, Tablespoon