Flat rate envelope sizes
The Priority Mail Flat Rate Envelope measures 12-1/2" x 9-1/2". In centimeters that is about 31.8 × 24.1 cm. Because an envelope wraps around what's inside, a thicker item uses up length and width: an item 1 in. thick can be at most about 11.5 × 8.5 in.
Flat rate envelope price
| Where you buy postage | Price |
|---|---|
| Online label (USPS.com, shipping apps) | $11.97 |
| Post Office counter | $13.90 |
The price is the same to every address in the 50 states, whether it weighs 2 ounces or 70 pounds. Buying the label online saves $1.93 per package. These are the prices in USPS Notice 123, effective October 4, 2026; USPS updates them each January and July, and the packaging itself is free.
Flat rate envelope shipping cost
Here is what a parcel of the same size would cost by USPS Ground Advantage (online label) at different weights and distances. Green cells are where the Flat Rate Envelope at $11.97 is cheaper.
| Weight | Ground, zone 2 | Ground, zone 5 | Ground, zone 8 |
|---|---|---|---|
| 8 oz | $7.34 | $8.24 | $8.95 |
| 1 lb | $8.08 | $9.29 | $11.22 |
| 2 lb | $8.48 | $10.50 | $13.42 |
| 5 lb | $10.41 | $14.53 | $20.24 |
| 10 lb | $12.91 | $17.81 | $26.39 |
| 20 lb | $18.11 | $26.68 | $42.14 |
Going cross-country (zone 8), the Flat Rate Envelope beats Ground Advantage from about 2 lb. For a nearby address (zone 2) it takes about 10 lb before flat rate wins. The calculator above does this comparison for your exact item and zone.
What fits in a flat rate envelope?
Typical things people send in it: documents and photos, a folded T-shirt, a paperback book, phone cases and small flat accessories.
From our presets, these fit: video game (6.75 × 5.25 × 0.5 in).
Too big for it: shoebox (no flat rate option — use Ground Advantage); hoodie (fits the Medium Box (Side-Loading)); 3 books (fits the Medium Box (Top-Loading)); laptop (fits the Medium Box (Side-Loading)); phone (fits the Padded Flat Rate Envelope).
The item must fit with the flap closing normally — USPS does not allow taping a flat rate envelope wider or taller to squeeze more in.
Frequently asked questions
How much is a flat rate envelope in 2026?
$11.97 with an online label and $13.90 at the Post Office counter (USPS Notice 123, effective October 4, 2026).
Is there a weight limit for the flat rate envelope?
Yes, 70 lb — the same limit as all Priority Mail. Up to that, weight doesn't change the price.
Where can I get a flat rate envelope?
Free at any Post Office or ordered free from the USPS online store. You must use the official USPS Flat Rate packaging to get the flat price.
How long does a flat rate envelope take to arrive?
It ships as Priority Mail, which USPS schedules for 1–3 business days. Delivery times aren't guaranteed.