How Shape and Size Affect Prices
Different postage prices apply to postcards, letters, large envelopes (flats), and parcels. In general, the bigger your mailpiece, the more it will cost to mail.
In First-Class Mail, postcards cost less than letters. Letter size mail costs less than flat-size mail. Parcels pay the highest price due to the cost of processing and delivery.
In USPS Marketing Mail, there is no postcard price. You can mail postcard-sized pieces as USPS Marketing Mail, but you'll pay the same as a letter. Letters cost less than large envelopes (flats). USPS Marketing Mail parcels (including tubes) are charged a higher price due to processing costs.
Can you get a better price by re-shaping your mailpiece? Possibly. You could fold your large envelope to be letter-sized, or you could redesign your parcel to qualify for the lower flat price.