Priority Mail Flat Rate Prices

Priority Mail Flat Rate envelopes cost $13.90 (standard), $14.25 (legal) and $15.00 (padded) and boxes cost $14.65 (small), $25.80 (medium) and $36.10 (large) at retail in USPS Price List Notice 123 effective October 4, 2026; the APO/FPO/DPO Flat Rate Box is $34.65 and Priority Mail Express Flat Rate envelopes are $38.25 to $39.25.

Maintained by Archie Chang · Sources checked against USPS text on November 2, 2026 · Methodology & sources

Not an official source. FedRateCalc is independent and is not affiliated with the U.S. Postal Service (USPS). USPS.com and your Post Office are the authority for prices and mailing rules. The prices here are the retail prices in USPS Price List Notice 123, effective October 4, 2026, read from an Internet Archive copy on November 2, 2026; commercial prices are listed separately in Notice 123 and are not shown. Figures marked as arithmetic are our own calculations from the table.

Priority Mail Flat Rate prices

Priority Mail Flat Rate retail prices in Notice 123, with the size printed there
Item	Size as printed	Retail price	Note
Flat Rate Envelope	12-1/2" x 9-1/2" or smaller	$13.90	—
Legal Flat Rate Envelope	15" x 9-1/2"	$14.25	Packaging only available at USPS.com.
Padded Flat Rate Envelope	12-1/2" x 9-1/2"	$15.00	Packaging only available at USPS.com.
Small Flat Rate Box	Inside 8-5/8" x 5-3/8" x 1-5/8"; outside 8-11/16" x 5-7/16" x 1-3/4"	$14.65	—
Medium Flat Rate Boxes	Inside 11" x 8-1/2" x 5-1/2"; outside 11-1/4" x 8-3/4" x 6" Inside 13-5/8" x 11-7/8" x 3-3/8"; outside 14-1/8" x 12" x 3-1/2"	$25.80	—
Large Flat Rate Box	Inside 12" x 11-3/4" x 5-1/2"; outside 12-1/4" x 12" x 6"	$36.10	—
APO/FPO/DPO Flat Rate Box	Inside 12" x 11-3/4" x 5-1/2"; outside 12-1/4" x 12" x 6"	$34.65	—

Sizes are copied as Notice 123 prints them; the Flat Rate box sizes page sorts them. When we checked on November 2, 2026, the USPS.com Priority Mail page listed the Flat Rate Envelope at $13.90 at a Post Office, the same retail price as Notice 123.

“Packaging only available at USPS.com.”

USPS Price List Notice 123, effective October 4, 2026, Flat Rate—Domestic footnote 1

Priority Mail Express Flat Rate envelopes

Priority Mail Express Flat Rate retail prices in Notice 123, with the size printed there
Item	Size as printed	Retail price	Note
Flat Rate Envelope	12-1/2" x 9-1/2"	$38.25	—
Legal Flat Rate Envelope	15" x 9-1/2"	$38.55	—
Padded Flat Rate Envelope	12-1/2" x 9-1/2"	$39.25	Packaging only available at USPS.com.

Priority Mail Express Flat Rate has envelopes only. For the DMM rule on them:

“Only USPS-produced Flat Rate Envelopes are eligible for the Flat Rate price, and only customers when using them are charged a flat rate, regardless of the domestic destination or actual weight (up to 70 pounds) of the mailpiece. Customers must only use USPS-produced Flat Rate Envelopes at the applicable Flat Rate Envelope price. Restrictions apply for using USPS-produced packaging (see 601.6.1).”

USPS Domestic Mail Manual 113, section 1.4

The Priority Mail Express cost page has the weight and zone prices.

What USPS requires for the Flat Rate price

“Only USPS-produced Flat Rate Envelopes or Flat Rate Boxes are eligible for the Flat Rate price, and only customers when using them are charged a flat rate, regardless of the domestic destination or actual weight (up to 70 pounds) of the mailpiece. Customers must only use USPS-produced Flat Rate containers at the applicable Flat Rate price. Restrictions apply for using USPS-produced packaging (see 601.6.1).”

USPS Domestic Mail Manual 123, section 1.4

“All USPS-produced Priority Mail envelopes smaller than the EP14F envelope (9.5 inches by 12.5 inches) are eligible for the Priority Mail Flat Rate Envelope price whether or not they are marked “Flat Rate Envelope.””

USPS Domestic Mail Manual 123, section 1.4.1

“Priority Mail Flat Rate Boxes are as follows:
Small Flat Rate Box to domestic, APO/FPO, and DPO destinations.
Medium Flat Rate Boxes (FRB-1) or (FRB-2) to domestic, APO/FPO, and DPO destinations.
Large Flat Rate Box to domestic destinations.
Large Flat Rate Box and “special version of this box” identified with the additional logo: “Americasupportsyou.mil.” to APO/FPO and DPO destinations. This box is priced less to mail than the conventional domestic Large Flat Rate Box. If the special version of the APO/FPO Flat Rate Box is used for non-APO/FPO and DPO destination addresses, domestic or international Large Flat Rate Box prices will apply.”

USPS Domestic Mail Manual 123, section 1.4.2

On extra fees for large packages, USPS.com says:

“USPS Flat Rate packaging is exempt from all Nonstandard Fees”

USPS.com Priority Mail page, read November 2, 2026

Packaging that is not USPS-produced Flat Rate packaging is priced by weight and zone; see how much Priority Mail is.

Other Flat Rate items on USPS.com

Also listed on the USPS.com Priority Mail page, with the price and sizes as USPS.com prints them (not in the Notice 123 Flat Rate table)
Item	Price on USPS.com	Size as printed
Window Flat Rate Envelope	$13.90 at Post Office & Online	10″ x 5″ 12 1/2″ x 9 1/2″
Small Flat Rate Envelope	$13.90 at Post Office	10″ x 6″
Large Flat Rate Board Game Box	$36.10 at Post Office	Outside: 24 1/16″ x 11 7/8″ x 3 1/8″ Inside: 23 11/16″ x 11 3/4″ x 3″

Frequently asked questions

How much is a Priority Mail Flat Rate envelope?

At retail, Notice 123 lists $13.90 for the Flat Rate Envelope, $14.25 for the Legal Flat Rate Envelope and $15.00 for the Padded Flat Rate Envelope. Notice 123 marks the legal and padded envelopes with the note “Packaging only available at USPS.com.”

How much is a Priority Mail Flat Rate box?

Notice 123 lists $14.65 for the Small Flat Rate Box, $25.80 for the Medium Flat Rate Boxes and $36.10 for the Large Flat Rate Box at retail. Each box has one price in the table, and the USPS rules for using Flat Rate packaging are quoted on this page.

Does weight change the Flat Rate price?

DMM 123 section 1.4 says only customers using USPS-produced Flat Rate packaging are charged a flat rate, regardless of the domestic destination or actual weight (up to 70 pounds) of the mailpiece.

Can I use my own box at the Flat Rate price?

DMM 123 section 1.4 says only USPS-produced Flat Rate Envelopes or Flat Rate Boxes are eligible for the Flat Rate price. Other packaging is priced by weight and zone, as on the “How Much Is Priority Mail?” page.

How much is a Priority Mail Express Flat Rate envelope?

Notice 123 lists $38.25 for the Flat Rate Envelope, $38.55 for the Legal Flat Rate Envelope and $39.25 for the Padded Flat Rate Envelope at retail.

Is there a Flat Rate box for APO, FPO and DPO addresses?

Notice 123 lists an APO/FPO/DPO Flat Rate Box at $34.65, against $36.10 for the Large Flat Rate Box. DMM 123 section 1.4.2 says the special version of the box is priced less, and that if it is used for non-APO/FPO and DPO destination addresses, domestic or international Large Flat Rate Box prices apply.

Are Flat Rate boxes exempt from extra fees for large packages?

USPS.com says “USPS Flat Rate packaging is exempt from all Nonstandard Fees”.