Depending on your route, your baggage allowance may be calculated by piece or weight.
On routes that include stops in the USA or Canada, your baggage allowance will be calculated by piece. You will be able to bring a fixed number of items, each of which must weigh under a certain weight.
For all other routes, your baggage will be calculated by weight. You will be allowed to take any number of items with a combined total weight under an amount determined by your route, class and member tier.
You can check the details of free baggage allowance for any flights.