Length

• Most stamps are longer than they are wide because a rectangle fits well on a sheet for sale in bulk. Buyers typically purchase stamps by the book, or 20 stamps at a time. A basic rectangular stamp is one-inch long or 22mm.
  
  

Width

• A rectangular stamp is only slightly smaller in width than length, measuring 7/8 inch or 19mm wide. When you purchase stamps on a long rectangular sheet, they come in two columns of 10 rows of stamps. As of June 2011, the cost of a basic first-class stamp is 44 cents.
  
  

Commemorative

• Commemorative stamps featuring holidays, famous people, events or charities deviate from the standard sizes and are often larger to add emphasis. The extra proceeds gained when purchasing special stamps go toward a specific cause or effort, such as breast cancer research or disaster relief fund. Commemorative stamps measure 36mm long by 22mm wide.
  
  

Custom Stamps

• You can also order stamps from companies with your own logos and pictures for a completely custom appearance. Sites include stamps ranging from small squares to large rectangles; some stamps in the past were in shapes such as a circle or star.