What's the Cheapest Way to Ship with USPS?

The cheapest way to ship with USPS depends on your package's weight and size, but three services cover almost every order: USPS Ground Advantage for light packages, Priority Mail Flat Rate for heavier items that fit a free box, and Priority Mail Cubic for small, dense ones. Here's how to pick between them.

Light packages: USPS Ground Advantage

For packages up to about a pound, USPS Ground Advantage in your own packaging is almost always the cheapest option. It launched in July 2023 and replaced First-Class Package Service, Retail Ground, and Parcel Select Ground, so if you remember shipping packages “First Class,” this is the service that took its place. Ground Advantage covers 1 oz to 70 lbs, delivers in 2 to 5 business days, and includes tracking and $100 of insurance at no extra charge.

Heavier packages that fit a box: Priority Mail Flat Rate

Once a package clears a pound or so, check whether it fits a Priority Mail Flat Rate Envelope or the Small Flat Rate Box. If it does, Flat Rate ships it anywhere in the country for one price, no matter the weight or distance, which makes it the cheap choice for dense items headed a long way. Medium and Large Flat Rate Boxes only pay off when a package is genuinely heavy, roughly over 20 lbs, and traveling across the country.

Small, dense packages: Priority Mail Cubic

If a package is heavy for its size and doesn't fit a Flat Rate box, Priority Mail Cubic is usually cheapest. Cubic prices by the box's outer dimensions instead of its weight, so a small, heavy package ships for far less than a weight-based rate would cost. Packages have to measure half a cubic foot or less, weigh 20 lbs or less, and be no longer than 22 inches on the longest side. The catch: Cubic pricing isn't sold at the Post Office counter, so you get it through shipping software or a 3PL. (More on how Cubic works.)

Two old money-savers that are gone

If an older guide points you to First-Class Package Service for parcels or a Priority Mail Regional Rate Box, it's out of date. USPS folded First-Class Package Service into Ground Advantage in 2023 and discontinued Regional Rate Boxes that same year. Ground Advantage and Priority Mail Cubic now cover both of those cases.

A quick rule of thumb

Under a pound, use Ground Advantage in your own box. Over a pound and it fits a Flat Rate box, use Flat Rate. Small and heavy but doesn't fit, use Cubic. That covers the large majority of orders.

One seasonal note: from October 4, 2026 to January 17, 2027, USPS adds a temporary holiday price increase of $0.40 to $9.10 per package on Ground Advantage and Priority Mail, and $0.85 to $2.10 on Flat Rate envelopes and boxes, depending on zone, weight, and whether you pay retail or commercial prices.

Running this math on every order gets old fast, and it's the kind of thing a 3PL handles for you, so orders go out on the right service without you choosing it each time. See how Simpl prices fulfillment.