"How many stamps do I put on my letter / postcard?"

One of the most useful tools that I use when I write a letter or mail a postcard is the USPS Postage Price Calculator. Using this website, you can calculate the cost of postage for a package or a letter destined to be sent anywhere in the world!

Determining the number of postage stamps for postcards is easy:

Your standard post card:

Maximum size: "6 inches long by 4-1/4 inches high by .016 inch thick."

Your standard post-card will simply cost $0.28. In other words, slap one stamp on and you're good to go!

Larger postcards:
NOTICE: Not all postcards are made alike! Larger postcards do cost more to send than the standard 6 inch card.

"Maximum size: 11-1/2 inches long by 6-1/8 inches high by 1/4 inch thick."

Your larger postcards will run you a bit more money: $0.44. Apply the correct amount of postage and off it goes!

The only catch for a letter is that you need to know how much your letter weighs.

Fortunately, there are also fairly good ways of estimating the weight of a letter.

A standard piece of 8.5" X 11" paper weighs about .16 ounces.

Envelopes are a bit more tricky to estimate because there are so many different sizes. In general, if I'm sending a normal letter or greeting card I simply take for granted that it weighs about the same as two standard 8.5" X 11" pieces of paper.

In the end, all of this information is likely only useful for significantly larger and/or heavier mail. Your standard greeting card or letter simply requires a single stamp to get wherever it is headed in the United States.