A postage stamp is 3/4 inch x 1 inch.
Around 30 to 40 mm in dimension
Postage stamps come in a mind-boggling assortment of sizes. Typical sizes for stamps would mean anywhere between 10 to say 30 mm counting in each direction. These sizes appear to be largely the easiest to handle. You also find several countries employing restricted collection of dimensions, so as to simplify automated machinery which handles stamps.
Some remarkable stamps include the Penny Black (Britain) and the Basel Dove (Switzerland). The formed is prided as the planet's first-ever official adhesive postage stamp. It was on 1 May 1840 that the United Kingdom of Great Britain and Ireland issued the same.
You find that postage stamps are typically rectangles. Thus allows for efficiency in packing many stamps on a given sheet. You of course have horizontal as well as vertical designs. You can also discover several additional shapes of postage stamps like triangles, octagons, and even freeform shapes.