In 2011, all first-class U.S. Postal Service stamps became "Forever" stamps. Regardless of postage increases, you can still mail a letter up to 1 ounce using a Forever stamp. Although most basic stamps have similar physical dimensions, there is no single standard size of USPS stamps, and limited edition and designer stamps vary greatly in size.
Typical Stamp Measurements
The size of a recent typical, familiar American flag Forever stamp measures 22.10 mm x 24.89 mm, which is about 0.87 inches x 0.979 inches. Stamps featuring characters or themes generally have different measurements. For example, the Valentine's day "Love" stamp measures 30.2mm x 23.1 mm or 1.188 inches x 0.909 inches. The War of 1812 commemorative stamp is 39.6 mm x 31.1 mm or 1.559 inches x 1.244 inches. MLB All-Stars series of stamps measure 39.6 mm x 24.1 mm or 1.559 inches x 0.98 inches.
The USPS allows you to express your creativity by personalizing your own postage stamps through third-party websites. Through Zazzle.com, you can upload your own design or choose from existing templates to customize your stamps. The small stamp is 45.7 mm x 33.02 mm or 1.8 inches x 1.3 inches. The large stamp measures 53.3 mm x 33.02 mm or 2.5 inches x 1.5 inches. PictureItPostage prints a photograph of your choice on self-adhesive labels that measure 36.49 mm x 57.15 mm or 1.437 inches x 2.25 inches. Photo stamps made through Stamps.com are 48.26 mm x 35.56 mm or 1.9 inches x 1.4 inches.