Question: how many stamps do you need for first class mail?
Answer: You can use more than one Forever Stamp if you need to send a package or a letter that weighs more than an ounce. Each stamp is worth the current first-class rate (not what you paid for them). So if you paid $0.49 and the rate rises to $0.50, you can put two Forever Stamps on a package to get $1.00 worth of postage.