If your PO has an APC (automated postal center), use it. It will always calculate the proper postage to be 88 cents. It helps if you have something else that you are mailing at the same time that costs more than a dollar and buy the postage for it first, then get the stamps for bubble mailers as additional purchases. If you are only mailing one bubble envelope, the APC will insist that you must also buy a first class stamp to bring the amount charged to your credit or debit (select use as credit) card to over a required $1 minimum purchase.