In the U.S., one stamp usually covers a standard letter up to 1 ounce total, including the envelope and contents. That’s roughly 28 grams.

What that means

  • A normal single-page letter usually fits under the limit.
  • Around 4–5 sheets of standard printer paper in a regular envelope is often still close to the limit, depending on paper and envelope weight.
  • If the letter goes over 1 ounce, you need extra postage.

Quick rule

If you’re unsure, treat 1 ounce as the safe maximum for one standard Forever stamp in the U.S..

Practical tip

A folded card, photo, or thick paper can push it over the limit faster than you might expect.

TL;DR

One stamp covers up to 1 oz for a standard U.S. letter.