The size decides the number. The country does not, except when its own listing adds a rule the general page never mentions.
The full flat rate ladder, group by group
USPS assigns every destination a flat rate price group, and each group has its own column in the published retail price list. Same envelope, same 4 lb ceiling, eight different numbers. The group examples below were read from USPS's own country price group table on 2026-08-30.
| Price group | Flat Rate Envelope | Small Box | Medium Box | Large Box |
|---|---|---|---|---|
| 1 (Canada) | 32.65 USD | 33.75 USD | 61.80 USD | 75.15 USD |
| 2 | 48.80 USD | 50.45 USD | 90.85 USD | 102.55 USD |
| 3 (India) | 49.75 USD | 51.40 USD | 96.40 USD | 121.30 USD |
| 4 (Ireland) | 54.55 USD | 56.35 USD | 93.15 USD | 110.60 USD |
| 5 | 52.30 USD | 54.00 USD | 95.95 USD | 108.85 USD |
| 6 | 53.00 USD | 54.75 USD | 112.70 USD | 139.55 USD |
| 7 | 62.35 USD | 64.45 USD | 133.10 USD | 155.00 USD |
| 8 (Iceland, Iran) | 50.55 USD | 52.20 USD | 102.55 USD | 132.05 USD |
Priority Mail Express International runs its own single flat rate envelope on the same group structure: 62.70 USD to group 1, 79.80 USD to group 3, 89.20 USD to group 6 and 102.50 USD to group 7, capped at 4 lb, read from usps.com/business/prices/2026/s-pmei-retail.csv on 2026-08-30. Note that the ladder is not a distance ladder — group 8 undercuts groups 4 through 7 on every line — so the group table is the only way to know which number applies.
USPS states Priority Mail Express International's delivery window as 3 to 5 business days and Priority Mail International's as 6 to 10 business days to many major markets, on both the flat rate and weight-based sides of each service. Customs holds sit outside both figures and are not something either page's day range accounts for.
What the USPS sentence actually excludes
USPS's own Priority Mail International page carries this line: “Except for Priority Mail International Flat Rate pricing, Priority Mail International prices are based on weight and destination country.” It is easy to read that as flat rate escaping the destination too. It does not. The same page footnotes its flat rate figures with “Prices are based on regional destination”, and the retail price file prints a separate flat rate column per group. What flat rate drops is the weight half of that pair: the box costs the same at 8 oz as at its ceiling. The weight-based alternative starts at 43.55 USD and climbs on both axes at once.
The same split exists on the Express side. Priority Mail Express International Flat Rate runs 62.70 USD to group 1 and 102.50 USD to group 7, ignoring weight up to 4 lb either way, while the weight-based version of the same service starts at 64.25 USD and moves on weight and group together.
Where the ceiling actually comes from
The 4 lb and 20 lb figures above are the general ceilings USPS prints on its main international product pages. They are not the last word. The USPS International Mail Manual keeps a separate page of country-by-country maximum weights, and its own individual country listings are where prohibitions and restrictions for a specific destination actually live, above and beyond whatever the general product page says.
Country limits can sit below the generic figure
Weight-based Priority Mail International's generic ceiling is 70 lb, but Albania's own listing caps it at 44 lb, and Algeria's at 44 lb as well — both read from the USPS International Mail Manual on 2026-08-30. Neither figure comes close to the 4 lb and 20 lb flat rate ceilings, but the pattern is the same one that eventually does: the country's own page, not the general one, sets the true maximum.
A country can close a door flat rate never mentions
Afghanistan's listing states that First-Class Mail International and First-Class Package International Service shipments may not contain dutiable articles at all — a restriction that exists nowhere on the general USPS page for either service. Priority Mail International, flat rate included, stays open to Afghanistan; the point is that a country's listing can shut a door the product page never hints at.
Check the destination before you tape the box
Nothing about a flat rate price tells you whether the destination accepts the contents. USPS's own guidance is that prohibitions and restrictions specific to a country appear under that country's listing, not under the service description, so the flat rate ladder above answers price and ceiling and leaves mailability to a separate lookup.
The domestic envelope against the international ladder
The same Flat Rate Envelope sold for domestic Priority Mail is 12.90 USD at the Post Office, per usps.com on 2026-08-30, against 32.65 USD for the cheapest international group and 62.35 USD for the dearest. What decides whether flat rate beats a weight-based label on the domestic side is covered on its own page rather than repeated here: see flat rate against weight-based shipping for the live comparison, and flat rate box prices for every domestic size and price.
SMKlog's checkout prices and prints domestic parcel labels, plus international labels to Canada, the UK, Germany and Australia with the customs declaration completed at checkout; other countries go through a manual review. What USPS, FedEx and UPS actually sell for shipments leaving the country, and the forwarder pattern that routes an overseas order through a US address on an ordinary domestic label instead, is the full subject of USPS international shipping, priced and explained. Customs paperwork itself is covered in customs forms and HS codes.
Flat rate questions, international side
Is USPS international flat rate shipping the same price to every country?
No. Flat rate means the price ignores the weight, not the destination. USPS's own price file for 2026 carries a separate flat rate column for each of eight destination groups, and its product page footnotes the figures with “Prices are based on regional destination”. The Flat Rate Envelope runs 32.65 USD to group 1 and 62.35 USD to group 7 — the same envelope, the same 4 lb ceiling, nearly double the price.
What does a Priority Mail International Flat Rate Envelope cost?
Between 32.65 USD and 62.35 USD at the Post Office or online, depending on the destination's price group, read from USPS's 2026 retail price file on 2026-08-30. The 32.65 USD figure quoted on the product page is the group 1 price, which covers Canada. The 4 lb ceiling and the 12 1/2 x 9 1/2 inch envelope are the same in every group.
What are the weight limits on USPS worldwide flat rate?
4 lb for the Flat Rate Envelope and the Small Flat Rate Box, 20 lb for the Medium and Large Flat Rate Boxes. USPS's own Priority Mail International page states those figures directly, and an individual country's own listing can still add restrictions on top of them, so the general ceiling is not a promise that every destination allows it.
Is there a flat rate version of Express Mail International?
Yes. Priority Mail Express International Flat Rate is an envelope capped at 4 lb, priced 62.70 USD to group 1 and up to 102.50 USD to group 7, checked 2026-08-30. The weight-based version of the same service starts at 64.25 USD and moves on weight as well as group.
Does a country's own listing ever override the general flat rate rules?
It can add restrictions the general product page never mentions. Afghanistan's listing in the USPS International Mail Manual states First-Class Mail International and First-Class Package International Service shipments may not contain dutiable articles at all, something the general USPS pages for those services do not say. Priority Mail International stays open there. The country listing, not the general product page, is what actually governs a given destination.
Where these figures come from
- USPS, Priority Mail International — Flat Rate Envelope and box prices, weight ceilings, and the weight/destination pricing statement. Read 2026-08-30.
- USPS, Priority Mail Express International — Flat Rate price and weight ceiling, weight-based starting price. Read 2026-08-30.
- USPS, Priority Mail (domestic) — domestic Flat Rate Envelope price. Read 2026-08-30.
- USPS, International Mail Manual, Country Price Groups and Weight Limits — general flat rate weight ceiling footnotes. Read 2026-08-30.
- USPS, International Mail Manual, Afghanistan listing — dutiable-article restriction on First-Class Mail/Package International. Read 2026-08-30.
- USPS, International Mail Manual, Albania listing — country maximum weights below the generic ceiling. Read 2026-08-30.
- USPS, International Mail Manual, Algeria listing — country maximum weight and customs form requirement. Read 2026-08-30.
USPS revises prices, ceilings and country listings without notice. Treat the figures above as what USPS published on the date shown, and check the individual country listing for the destination actually on the label.