$1.00 Stamps for Large Envelopes
In 2020 you'll need a $1.00 stamp to mail any of the following first-class letters:
- 1st class large envelope, 1 oz
- 1st class, 3 oz - odd size
- 1st class, 3.5 oz
Letters are considered "large envelopes" or "flats" if they measure greater than 6-1/8 inches high OR 11-1/2 inches long OR 1/4 inch thick.
If your letter weighs 3 oz but is also odd-sized/non-machinable you'll need a $1.00 stamp.
This weight/size combination is quite rare but the post office does have a rate for it.
You can determine if your wedding invitation is a standard letter or a large envelope by using our postage calculator, but be sure to double-check the weight of your invitations with your local USPS post office before ordering postage online.