The cost for mailing a letter depends on a number of factors: how much it weighs, the size of the letter, and the letter's destination. Knowing how much the letter weighs will help you calculate how much it will cost to mail it. The most accurate method for weighing a letter is to use a postal scale. These scales weigh in very small increments, which is best suited for light objects such as letters and are available in both analog and digital varieties. A digital postal scale will provide the most precise reading, which will help you more accurately calculate the weight and cost for mailing your letter. If you will be weighing letters or packages frequently, you may want to consider purchasing your own postal scale.
Purchase a postal scale and read the instructions carefully. If you don't wish to purchase your own postal scale, you can use the scales that are available for public use at your local Post Office.
Place the letter you want to mail inside the envelope. You will need to weigh both the letter and the envelope together to get the entire weight for calculate mailing costs.
Look at the readout on the scale before you place your letter on it. Ensure that it displays 0 oz. If the weight shown is more or less than this, then you'll have to take this difference into account after you place your letter on the scale and add it to or subtract it from the weight of the letter. If you own the postal scale you will be using, and the readout is not 0 oz. when it's empty, be sure to calibrate the scale according to the instructions that came with it before weighing your letter.
Turn on the scale (if it's digital) and place your letter and the envelope on the scale. The weight will display on the screen.
Read the weight and write it down on a piece of paper. You can now use this weight to determine postage costs for mailing your letter.