What makes something a parcel?
How USPS and Canada Post classify letters, flats, and parcels — and why the line between them determines what you pay.
Letter, flat, or parcel
In both USPS and Canada Post systems, mail is classified as a letter, flat (large envelope), or parcel. A parcel is any mailpiece that exceeds flat dimensions — typically anything over 15 inches long, 12 inches high, 0.75 inches thick, or heavier than 13 ounces (USPS) or 500g (Canada Post).
Classification determines which postal service applies and what that service costs. A 14-ounce padded envelope that just misses flat classification ships as a parcel (minimum ~$7 via USPS Ground Advantage) rather than as a flat (~$3.99 First-Class Mail). Understanding where your package falls is the fastest way to find cost savings.
| Class | Max size (USPS) | Max weight |
|---|---|---|
| Letter | 11.5" × 6.125" × 0.25" | 3.5 oz |
| Flat (large envelope) | 15" × 12" × 0.75" | 13 oz |
| Parcel | 130" (L + girth) | 70 lbs |
USPS classification. Canada Post uses 500g and 380×270×20 mm as the letter→parcel threshold. Full letter and flat classification guide →
Once a package clears the parcel threshold, the next question is which service to use. See USPS parcel service options →
Compare all carriers before your next shipment
See USPS, UPS, FedEx, Canada Post, Purolator, and more side by side — with known surcharges and DIM weight calculated before you print.