Stamp (postage) Amount Calculator. Now you can select 18 kinds of stamps (one cent to one dollar) from the pulldown menu. It also supports the new postage amount (37 cents for the first class letter, effective by June 30, 2002). This program can calculate your stamp amount for U.S. domestic letter and first class letter via airmail from United States to the overseas countries (include Canada and Mexico). You can select the weight unit between gram (metric) and ounce (oz). Just tap the unit name and select one you want to use. You can also select the destination country as USA, Canada, Mexico and other countries.