As of June 2014, a single First-Class Mail International stamp provides ample postage for a postcard heading to Brazil. The delivery time for this item varies based on the destination within Brazil and where the postcard originated in California.
All international mail pieces that weigh 1 ounce or less need a single international stamp. The stamp provides postage for more than 180 countries, including Brazil. For clarification purposes, USPS Global Forever stamps are round, whereas domestic stamps are square in shape. After the postcard arrives at its international destination, the local postal system takes control of the item and delivers it to the recipient.