To determine how many stamps to put on a large envelope, the sender must first weigh the envelope with the contents inside and measure it to be sure it conforms to USPS large envelope specifications. Next, the sender should type in the point of origin and destination on the USPS online postage price calculator. The calculator gives prices for various options of service based on security and speed.
As of September 2014, USPS defines large envelopes as those with minimum dimensions of 6 1/8 inches by 11 1/2 inches and maximum dimensions of 12 inches by 15 inches. The envelopes also must be a maximum of 3/4 inches thick. Mail sent to international destinations needs more postage than mail sent to domestic destinations.
Large envelopes can be sent via priority mail express, priority mail and first class mail as of September 2014. Priority mail express is quickest, and the base fee includes mail tracking and insurance for up to $100. Priority mail is faster than first class mail. For additional fees, more services can be added to the basic postage rate, including insurance against loss or damage for up to $5,000, USPS tracking, signature confirmation of delivery and certified mail. The most secure method of mailing is registered mail, which includes proof of mailing, confirmation of delivery or attempted delivery, and insurance up to $25,000 based on the value of the contents.