If you're trying to calculate postage rates at home, buying a postage scale may seem important. However, you can easily figure out what the United States Postal Service, USPS, will charge to mail a package without one. Keep a few principles in mind and you will quickly learn how to calculate U.S. rates without a postage scale.
Items you will need
Measuring tape or string
Pack and seal your box or envelope so it is ready to go. To get an accurate rate, you will need to weigh it as it is going to be shipped.
Calibrate your kitchen scale so the needle is slightly to the right of zero. This will ensure that even if you miscalculate slightly, you will still have enough postage to get your package to its destination.
Place your box, envelope or tube onto your makeshift postage scale. Make sure nothing supports it but the scale itself.
Write down the weight of the package when the needle stops moving. It is always a good idea to round up to the nearest ounce. If the package weighs 13 ozs. or less, you can use First-Class Mail, if using stamps. If it weighs more than 13 ozs., you will have to ship it another way through USPS, such as Express Mail, Parcel Post or Priority Mail.
Calculate the size of any boxes you are shipping. Use a measuring tape and measure the length, width and height of the box. Write down these dimensions too.
Use the USPS postage rate online calculator (see Resources) to figure out how much it will cost to ship your mail. Once you're on the website, enter the destination (U.S. or International), starting and ending zip code, mailing date and weight.
Click on the correct package type, if you are shipping anything other than a box. However, if it is a box but you are unsure if it is considered a "package" or "large package," select "large package" as the type. You will have an extra step before you get to view the list of postage rates where you can enter your box's exact dimensions.
Click "Continue" and you will get a list of USPS postage rates for your package. Double-check the criteria for First-Class Mail Package Rates. These are still cheaper than Priority Mail but perhaps slightly higher than First-Class postage.
Affix the correct amount of stamps on your package if you meet USPS criteria for First-Class Mail. Each stamp was 44 cents at the time of publication. For example, if the postage cost for your package is $3.08, you will need seven First-Class stamps.
Purchase and print the postage online if your package requires a higher class of mail. The rate you pay will depend upon your desired arrival time.
If you do not have a tape measure, measure the length, width and height of your box or envelope with a piece of string or yarn. Then compare the string to a ruler to determine the dimensions of the box.