US domestic First-Class postage calculator · October 2026 edition

Confirm the mailpiece requirements

Measurements are in inches and ounces. For this calculator, the piece must be rectangular and prepared according to USPS rules. Postcards must be unfolded, uncreased, uniformly thick paper/card stock with permitted attachments. Flats must be flexible and uniformly thick. Rigid or uneven large envelopes need parcel pricing.

For letters, report any additional nonmachinable feature: a plastic/nonpaper exterior, clasps or strings, uneven or loose contents, excessive rigidity, an address parallel to the shorter dimension, or other DMM 101.1.2 preparation criteria. This calculator separately checks the length-to-height ratio and the thin oversized-letter rule. A surcharge cannot make a nonmailable piece acceptable.

This tool covers domestic single-piece retail First-Class Mail. Use the official USPS calculator for parcels, other services, international items or uncertain classification. It does not sell postage.