Flat rate shipping charges one price per package size instead of by weight; USPS, UPS and FedEx each offer it, with different rules.
The United States Postal Service (USPS) has Priority Mail Flat Rate, United Parcel Service (UPS) has UPS Simple Rate, and FedEx has FedEx One Rate. USPS takes up to 70 lbs in its own free boxes, UPS lets you use your own box up to 50 lbs, and FedEx covers express services in FedEx packaging. All three are cheapest for dense, heavy items and can cost more than weight-based rates for light packages.
What is flat rate shipping?
Flat rate shipping is a carrier pricing option where the package size, not its weight or distance, sets the price, within a weight limit.
Businesses use it because the cost is known before the order ships:
- Predictable costs: one price per box makes it easy to show shipping at checkout or offer free shipping.
- Less work: no weighing each package or looking up zones, as long as it is under the weight limit.
- Free packaging: USPS and FedEx supply their flat rate boxes and envelopes for free.
The trade-offs are just as clear:
- You can overpay on light items: a 1 lb package going nearby is often cheaper by weight.
- Limited packaging: USPS and FedEx require their own boxes, and every carrier has a size cap.
How do USPS, UPS and FedEx flat rates compare?
USPS Flat Rate allows the most weight and ships abroad, UPS Simple Rate uses your own box, and FedEx One Rate has the most express options.
| Feature | USPS Priority Mail Flat Rate | UPS Simple Rate | FedEx One Rate |
|---|---|---|---|
| Packaging | USPS Flat Rate envelopes and boxes only (free) | Your own box or poly mailer | FedEx One Rate packaging only (free) |
| Weight limit | 70 lbs | 50 lbs | Under 50 lbs (boxes, paks, tubes); under 10 lbs (envelopes) |
| Size limit | Must fit the USPS box or envelope | 1,728 cubic inches (1 cubic foot) | Must fit the FedEx packaging |
| Price depends on | Packaging only | Size tier (Extra Small to Extra Large) and service | Packaging, service and zone |
| Services | Priority Mail (2 to 3 days); also Priority Mail Express Flat Rate Envelopes | UPS Ground, UPS 3 Day Select, UPS 2nd Day Air, UPS Next Day Air Saver | FedEx Express Saver, 2Day, 2Day A.M., Standard Overnight, Priority Overnight, First Overnight |
| International | Yes, Priority Mail International Flat Rate | No, U.S. only | No, U.S. domestic only |
| Lowest published price | $11.97 Commercial ($13.90 retail), Flat Rate Envelope | $12.20, Extra Small by UPS Ground | $12.75, FedEx Envelope by Express Saver or 2Day |
How much does USPS Flat Rate cost?
USPS Flat Rate costs $11.97 to $32.75 at Commercial prices and $13.90 to $36.10 at the Post Office, the same to any U.S. address.
| USPS packaging | Post Office (retail) | Commercial (online) |
|---|---|---|
| Flat Rate Envelope | $13.90 | $11.97 |
| Small Flat Rate Box | $14.65 | $12.95 |
| Medium Flat Rate Box | $25.80 | $22.02 |
| Large Flat Rate Box | $36.10 | $32.75 |
These prices include a temporary holiday increase that ends on January 17, 2027. Every box size, the legal and padded envelopes, international prices and the packaging rules are in our USPS Flat Rate guide, and you can ship online from the USPS Flat Rate shipping page.
How much does UPS Simple Rate cost?
UPS Simple Rate starts at $12.20 for an Extra Small package by UPS Ground and goes up with the package size and the speed of service.
You measure your own box (length x width x height in inches) to find its size tier, then pay that tier's price for the service you choose. You do not need a UPS account or contract to use it.
| UPS Simple Rate size | Package size | UPS Ground |
|---|---|---|
| Extra Small | 1 to 100 cubic inches | $12.20 |
| Small | 101 to 250 cubic inches | $15.80 |
| Medium | 251 to 650 cubic inches | $18.95 |
| Large | 651 to 1,050 cubic inches | $24.85 |
| Extra Large | 1,051 to 1,728 cubic inches | $30.95 |
Air services cost more for the same size. Retail prices at a UPS counter are also higher: $13.00 for Extra Small and $16.00 for Small by UPS Ground. A package over 50 lbs or 1,728 cubic inches is priced at standard UPS rates instead. More on our UPS flat rate shipping page.
How much does FedEx One Rate cost?
FedEx One Rate starts at $12.75 for a FedEx Envelope by FedEx Express Saver or FedEx 2Day, and those two services cost the same in every zone.
| FedEx packaging | Express Saver or 2Day (all zones) | Standard Overnight, Zone 2 | Standard Overnight, Zones 5 to 8 |
|---|---|---|---|
| FedEx Envelope | $12.75 | $31.20 | $37.90 |
| FedEx Extra Small Box | $13.40 | $32.70 | $39.60 |
| FedEx Pak | $16.30 | $36.30 | $44.00 |
| FedEx Small Box | $19.55 | $39.10 | $53.45 |
| FedEx Medium Box | $24.35 | $41.90 | $65.70 |
| FedEx Large Box | $32.05 | $56.40 | $87.95 |
| FedEx Extra Large Box or Tube | $42.75 | $74.50 | $110.20 |
Account discounts do not apply to One Rate prices. An envelope thicker than 3 inches or a pak thicker than 5 inches is rated as a box, and an on-call pickup costs $4. For how it works step by step, read what FedEx One Rate is.
Which flat rate service is cheapest?
For a dense, mid-weight package, UPS Simple Rate by Ground often has the lowest published price; USPS is close, and FedEx One Rate costs more.
Take a 10 lb item measuring 11" x 8-1/2" x 5-1/2":
- USPS: it fits the Medium Flat Rate Box 1, for $22.02 Commercial or $25.80 at the Post Office, delivered in 2 to 3 days to any U.S. address.
- UPS: in your own 12" x 9" x 6" box (648 cubic inches) it is a Simple Rate Medium, $18.95 by UPS Ground at daily rates.
- FedEx: it fits the FedEx Large Box (8-3/4" x 7-3/4" x 11-1/4"), for $32.05 by FedEx 2Day.
The answer changes with the package. An item over 50 lbs (up to 70 lbs) can only go flat rate with USPS. A package going abroad can only go flat rate with USPS. And for a light package going nearby, none of the three is likely to be cheapest: weight-based rates usually are.
Is flat rate shipping always cheaper?
No. Flat rate shipping is cheaper for heavy, compact items going far, but light packages and short trips usually cost less with weight-based rates.
With USPS, for example, a 2 lb package to a nearby zone costs $9.79 by weight at Commercial prices, against $12.95 in a Small Flat Rate Box. See the break-even weights for every USPS box in USPS Flat Rate vs Priority Mail, and compare the carriers more broadly in USPS vs UPS vs FedEx. More guides are in domestic shipping guides.
Shipping flat rate for a business? Shipixy gives you discounted UPS, FedEx and USPS rates, up to 75% off depending on the service, with no subscription fees. Compare carriers for your package with the shipping calculator or sign up to start shipping.
Sources
All sources were checked on October 25, 2026. Carriers change their prices; the official pages below always win.
- USPS Notice 123: price list, effective October 4, 2026
- USPS: Priority Mail and Flat Rate products
- USPS release: temporary price change for the 2026 holiday shipping season (August 25, 2026)
- UPS: flat rate shipping with UPS Simple Rate
- UPS: 2026 Rate and Service Guide, Daily Rates, updated September 7, 2026 (PDF)
- UPS: 2026 Rate and Service Guide, Retail Rates, updated September 7, 2026 (PDF)
- FedEx: FedEx One Rate
