How to Use the USPS Postage Calculator
Figuring out how many stamps to put on an envelope can be confusing once it weighs more than a single sheet of paper. This calculator takes your mail's weight in ounces and calculates the estimated USPS First-Class Mail letter postage.
USPS First-Class Mail letters start at $0.73 for the first ounce, with $0.28 for each additional ounce, up to a maximum of 3.5 oz. Beyond that weight, USPS requires you to mail it as a Large Envelope (flat) or Package instead, which follow a different rate structure entirely.
A standard single-page letter in a regular envelope typically weighs well under 1 oz, but stuffing in multiple pages, a greeting card, or a small enclosure can quickly push it into the 2 oz or 3 oz tier. Weighing your envelope on a kitchen scale before applying stamps is the most reliable way to avoid having mail returned for insufficient postage.
Keep in mind that this calculator reflects standard First-Class Mail letter rates only. Extra services such as Certified Mail, tracking, or Priority Mail use separate pricing, and USPS periodically updates its rates — so treat this as a helpful estimate and confirm exact pricing at usps.com or your local post office when it matters.
Frequently Asked Questions
First-Class Mail letters are capped at 3.5 oz. Heavier mail must be sent as a Large Envelope (flat) or Package, which use different rate structures.
This calculator uses standard First-Class Mail letter rates as a reference estimate. Extra services like tracking or certified mail, and periodic USPS rate changes, can affect your actual cost at the counter.