It buys a speed, not just a price
Every flat rate envelope travels as Priority Mail, which quoted 2-3 business days from Los Angeles to New York in our tables. Slower ground labels save cash on flat mail precisely because you accept a longer ride.
One envelope, one price
USPS Priority Mail flat rate envelope, priced and measured
The regular flat rate envelope runs $12.90 at the counter, the legal size $13.25, the padded $14.00, per usps.com, checked 2026-07-27. Same price to the next town or the far coast. Whether that beats an ordinary weight-based label depends entirely on what you stuff inside, and light contents usually say no.
Figures from usps.comQuotes dated, not recycledGuest checkout
Two sources, both named
Envelope prices come off usps.com; the weight-based rows below came out of our calculator the same day, 2026-07-27.
Every flat rate envelope USPS sells
Five envelope variants exist, though three share one price. Dimensions and figures below are quoted from usps.com as of 2026-07-27; USPS lists them all as holding up to 70 lb. Commercial pricing is what label platforms, ours included, pass through.
| Envelope | Size | Counter price | Commercial |
|---|---|---|---|
| Flat Rate Envelope | 12.5 × 9.5 in | $12.90 | $11.12 |
| Window Flat Rate Envelope | 12.5 × 9.5 in | $12.90 | $11.12 |
| Small Flat Rate Envelope | 10 × 6 in | $12.90 | $11.12 |
| Legal Flat Rate Envelope | 15 × 9.5 in | $13.25 | $11.66 |
| Padded Flat Rate Envelope | 12.5 × 9.5 in | $14.00 | $11.99 |
What the same shipments quoted by weight, 2026-07-27
We ran envelope-sized shipments through our calculator on the Newark, NJ (07102) to Atlanta, GA (30303) lane and the Los Angeles (90011) to New York (10001) lane. Totals shown are final checkout figures with SMKlog's cut already in them.
| Shipment | Lane | Best quote | Transit |
|---|---|---|---|
| Document mailer, 12.6 × 9.4 × 0.8 in, 7 oz | Newark → Atlanta | $8.38 USPS Ground Advantage | 5-6 business days |
| Same mailer, faster option | Newark → Atlanta | $11.39 UPS Ground | 2-3 business days |
| 1 lb box, about 10 × 8 × 4 in | Newark → Atlanta | $9.91 USPS Ground Advantage | 6-7 business days |
| 1 lb box, Priority Mail speed | Newark → Atlanta | $14.49 USPS Priority Mail | 4-5 business days |
| 1 lb box, about 10 × 8 × 4 in | Los Angeles → New York | $11.12 USPS Ground Advantage | 6-7 business days |
| 1 lb box, Priority Mail speed | Los Angeles → New York | $16.47 USPS Priority Mail | 2-3 business days |
Read those rows against the envelope table and a pattern falls out. Light contents lose money in a flat rate envelope; the 7 oz mailer shipped for $8.38 when the envelope wanted $12.90. Flip it around for weight and distance. A coast-to-coast Priority Mail quote for a 2 lb parcel came back at $22.34 on the western lane that day, and a stuffed legal envelope at $13.25 would have carried dense flat contents at Priority speed for much less. The flat rate is a bet that your contents are heavier than they look.
Bendable is the real limit
An envelope holds whatever lets it close: paper, soft goods, cards, a slim book. Rigid or chunky items belong in the flat rate boxes instead, which get their own price ladder on our flat rate box pricing guide.
Padded costs a bit more for a reason
The $14.00 padded version has bubble lining and a touch of depth, so slightly lumpy contents ride protected. For anything genuinely three-dimensional, measure it and let a quote decide the container.
Flat rate envelope questions
How much is a Priority Mail flat rate envelope?
Per usps.com, checked 2026-07-27: $12.90 at the counter for the regular, window and small versions, $13.25 for the legal size, $14.00 for the padded one. Commercial pricing through label platforms runs $11.12, $11.66 and $11.99 for those same three tiers.
What fits inside a flat rate envelope?
Anything bendable and flat: document stacks, folded clothing, thin paperbacks, trading cards in sleeves. The regular envelope measures 12.5 x 9.5 inches, legal stretches to 15 inches long, and the padded version has a little give for lumpy contents. USPS caps the weight at 70 lb, which paper almost never reaches.
Is the envelope cheaper than paying by weight?
Not for light contents. On 2026-07-27 a 7 oz document mailer from Newark to Atlanta quoted $8.38 with USPS Ground Advantage, well under the $12.90 flat price. The envelope earns its keep on dense contents heading across the country, where a weight-based Priority Mail quote climbs past it.
Do the envelopes cost anything at the Post Office?
The packaging itself is free. Grab envelopes in the lobby or order packs from store.usps.com at no charge; you pay only when you buy the postage.