How many stamps do I need per envelope?

Letters can be mailed using one single U.S.A. First-Class 49 cent stamp per envelope, according to the United States Postal Service. It's the amount of postage that matters, not the number of stamps, so any number of stamps with a total value of 49 cents is acceptable, as of 2014.

The 49 cent rate applies to letters weighing up to one ounce. Another 21 cents is added beyond the first ounce and for each ounce thereafter. Letters to international destinations that weigh less than an ounce require $1.15 postage.

The minimum letter-sized envelope is 5 inches long by 3 ? inches tall and the maximum is 11 inches long by 6 ? inches tall, as stated in the Postal Service?s customer?s guide to mailing.