When does a piece ship instead of mail?
Once a piece exceeds First-Class Mail limits (over 13 ounces, or a parcel), or is boxed/rigid, it moves to a shipping service. The main domestic options are USPS Ground Advantage, Priority Mail, and Priority Mail Express. See Parcel for what counts as a parcel.
What is USPS Ground Advantage?
USPS's primary ground service, which replaced Retail Ground, Parcel Select Ground, and First-Class Package Service. Packages up to 70 pounds, max 130 inches length plus girth, delivered in 2 to 5 business days. Every label includes USPS Tracking and $100 of insurance; more coverage is available up to $5,000. The mailer supplies the packaging. Ounce-based pricing applies up to about 16 ounces, then pound-based. Accepts hazmat. Certified Mail is not available on Ground Advantage. Cubic pricing (by size, not weight) is available for smaller dense packages. See DMM 253.
Priority Mail
Faster shipping, 1 to 3 business days, packages up to 70 pounds, max 108 inches length plus girth. Includes tracking and insurance (commonly $100 at commercial pricing). Flat Rate boxes and envelopes are available (one price regardless of weight or zone within limits), as is Cubic pricing. USPS provides free Priority Mail packaging. Certified Mail can be added. See DMM 223.
Priority Mail Express
USPS's fastest service, 1 to 2 days (overnight to most locations), with a money-back guarantee. Sunday and holiday delivery in many markets for an added fee. Up to 70 pounds. Use for urgent, date-critical items. See DMM 213.
How is dimensional weight calculated?
For packages larger than one cubic foot (1,728 cubic inches) shipping to farther zones, USPS bills the greater of actual weight or dimensional weight, computed as length x width x height divided by the DIM divisor. The divisor changed to 139 on July 12, 2026, which raises the billed weight on large, light packages. Oversized or irregular packages can carry nonstandard surcharges. Confirm the actual charge in the estimator, which prices from Notice 123.
Which USPS shipping service should I use?
Ground Advantage is the low-cost default (2 to 5 days). Priority Mail is faster (1 to 3 days) and offers Flat Rate. Priority Mail Express is for guaranteed, next-day-ish delivery. For a specific box, weight, and destination, the Postage Estimator returns the current Notice 123 price.