How many stamps for 6.3 ounces?

The number of stamps needed for mailing a 6.3-ounce letter depends on the mailing class and destination. For a standard First-Class Mail letter, the postage for a letter weighing over 1 ounce increases with each additional ounce. As of my last update, you would typically need at least two First-Class stamps or an equivalent amount in postage for that weight, but it's best to check with the latest USPS guidelines for accurate postage rates.