What sets the price
Weight, rounded up to the next pound (Ground Advantage has steps of 4, 8, 12 and 15.999 ounces under a pound). Distance, as a USPS zone from 1 (local) to 9, from USPS's zone chart for your two ZIP codes. And size: boxes over one cubic foot pay for dimensional weight if it's higher (length × width × height ÷ 166), and long or very large boxes pay extra fees.
Size fees
| If the box is… | Priority Mail and Express | Ground Advantage |
|---|---|---|
| Over 22 in long (up to 30) | +$4.50 | +$4.50 |
| Over 30 in long | +$21.00 | +$10.00 |
| Over 2 cubic feet | +$35.00 | +$21.00 |
| Over 108 in length + girth | Standard price | Oversized price |
Flat Rate can be cheaper
Priority Mail Flat Rate envelopes and boxes cost the same to any US address, up to 70 lb: $13.90 for the envelope, $14.65 small box, $25.80 medium and $36.10 large. For heavy items going far, a Flat Rate box often beats the weight-based price. The calculator tells you when one might.
Retail vs. online prices
These are retail prices, what you pay at the Post Office counter. Many online label services offer USPS's lower commercial prices, so if you ship often, compare them.
Where these prices come from
USPS Notice 123, effective October 4, 2026. That edition includes USPS's temporary holiday increase, in effect through January 17, 2027. Zones come from USPS's National Zone Charts Matrix. Alaska, Hawaii, territories and military addresses aren't covered yet; check usps.com for those.
Prices checked November 11, 2026.
Questions people ask
How much does it cost to mail a letter?
A standard 1 oz letter costs $0.82 with a Forever stamp, anywhere in the US. Each extra ounce adds $0.29, up to 3.5 oz. Square or rigid envelopes cost $0.49 more.
Is Ground Advantage cheaper than Priority Mail?
Usually, especially for light packages. For heavier items going far, Priority Mail, and especially a Flat Rate box, can cost about the same or less while arriving sooner.
Does USPS charge by size?
For boxes over one cubic foot, yes: USPS charges the greater of the actual weight and the dimensional weight (L × W × H ÷ 166). Long boxes and boxes over two cubic feet pay extra fees.