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 Standard Mail, there is no postcard price. You can mail postcard-sized pieces as Standard Mail, but you'll pay the same as a letter. Letters cost less than large envelopes (flats). Standard 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.
Tabbing and wafer seals for folded self-mailers
How weight affects prices
How distance affects prices
How quantity affects prices
Mail entry Point: Destination entry prices
Calculate postage for any class of commercial mail or price
Price List - Notice 123
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