The amount of postage needed to mail a 6” x 9” envelope depends on the postal classification rate used for shipping. When mailing to an address within the US, the most popular service is First Class; Priority Mail Flat Rate costs more for shipping a few ounces, but can be less expensive if the envelope is over 3.5 ounces in weight or ¼ inch in thickness; and Priority Mail Express Service offers a flat rate fee that includes several extra services at no additional costs.
FIRST CLASS MAIL
A 6” x 9” envelope with weight up to 1 ounce requires one $.49 first class rate stamp; weight between 1 and 2 ounces will cost $.70; weight between 2 and 3 ounces will cost $.91; and weight between 3.0 and 3.5 ounces will cost $1.12. Envelopes that exceed 3.5 ounces in weight or are thicker than ¼ inch will be charged the larger envelope rates.
If the contents of the envelope have an important business or correspondence value to either the sender or receiver; there are additional postal services available for added fees based on the envelope size, shape and weight. The added services and the associated costs can be viewed in detail at https://www.usps.com/ship/ship-a-package.htm.
PRIORITY MAIL FLAT RATE
A 6” x 9” envelope will fit in a USPS Priority Mail 9-1/2” x 12-1/2” envelope and can be mailed for a domestic flat rate of $5.60. As with a first class mailing, the Priority Mail Flat Rate system offers additional services that include proof of mailing, protection wile in the postal system and confirmation of delivery. The extra costs can be viewed in detail at https://www.usps.com/ship/priority-mail.htm.
PRIORITY MAIL EXPRESS FLAT RATE SERVICE
A 6” x 9” envelope will fit in a USPS Priority Mail Express 9-1/2” x 12-1/2” and can be mailed for a domestic flat rate of $19.99. The price for this service includes proof of delivery, a tracking system and insurance coverage up to $100. Additional insurance coverage is available for a fee. The added costs can be viewed in detail at https://www.usps.com/ship/priority-mail-express-flat-rate.htm.
As a quick guide, only one first class stamp is needed to mail a 6” x 9” envelope anywhere within the United States if it weighs less than 1.0 ounce. For any added services or other mailing choices; the number of stamps needed will be dictated by the desired mailing rate chosen.
