The non-machinable mail surcharge is a $0.49 fee USPS adds to any First-Class letter that can’t safely pass through its automated sorting equipment. In 2026, that brings a one-ounce non-machinable letter to $1.27 total: the standard $0.78 First-Class rate plus the surcharge.1Postal Explorer. USPS Notice 123 Price List The surcharge applies regardless of weight, because the issue is shape and handling, not heaviness.2USPS.com. First-Class Mail Service
What Triggers the Surcharge
USPS sorting machines run letters at high speed through belts, rollers, and optical scanners. A letter that jams, snags, or tumbles gets pulled for manual sorting, and that’s what the surcharge pays for. Your letter only needs to hit one of the triggers below to qualify as non-machinable:3Postal Explorer. Domestic Mail Manual 101 – Physical Standards for Letters, Cards, Flats, and Parcels
- Aspect ratio outside 1.3 to 2.5. Divide the envelope’s length (the side parallel to the address) by its height. Square envelopes have a ratio of 1.0, which is why wedding invitations almost always get surcharged.4United States Postal Service. Publication 25 – 1-2.3 Aspect Ratio
- A non-paper exterior or plastic wrapping. Polybagged or polywrapped pieces can’t be machined. Clear windows on paper envelopes are fine.
- Clasps, strings, or buttons on the outside. Anything that could catch on rollers.
- Uneven thickness from what’s inside. Pens, keys, coins, wax seals, or any object that creates bumps and ridges.
- Too thin for the envelope’s size. Under 0.009 inches thick, if the piece is more than 6 inches long or more than 4¼ inches high.
- Too rigid to flex. Letters have to bend as they move through sorters. A cardboard insert or a thick photo can stiffen the whole envelope enough to trigger the surcharge.
How to Check a Letter Before You Mail It
A few seconds at the kitchen table saves the trip back to the post office.
- Squeeze it. Run your fingers across the envelope. Lumps, ridges, or shifting objects mean non-machinable.
- Flex it. Bend gently. Resistance or an internal crack means the piece is too rigid.
- Measure it. Length divided by height should land between 1.3 and 2.5.
- Look at the surface. Any external clasp, string tie, button, or non-paper material triggers the surcharge.
If you’re not sure, take the letter to a post office counter. A clerk can weigh and measure it on the spot.
How to Avoid the Surcharge
Square wedding invitations are the classic unavoidable case. Plenty of other letters, though, get surcharged only because of packaging choices that could have gone the other way.
Choose rectangular envelopes when the contents allow it. A standard No. 10 envelope (4⅛ by 9½ inches) has an aspect ratio around 2.3, well inside the machinable range. Many greeting cards come in rectangular envelopes for exactly this reason.
Skip metal clasps and string ties. A self-sealing flap or a plain adhesive seal keeps the outside smooth. If you want a decorative seal, place it on the back rather than using a raised wax seal that thickens the envelope unevenly.
For rigid contents like photos, think about whether letter-rate mailing is really the right choice. Sandwiching a photo between cardboard triggers the surcharge and can still leave the item damaged in processing. A flat-rate envelope or small parcel usually protects the contents better and often costs only slightly more.
Writing “Do Not Bend” on the outside doesn’t change anything. USPS classifies mail by physical characteristics, not by instructions written on the envelope. If the contents truly can’t bend, send them as a parcel.
The Non-Machinable Forever Stamp
USPS sells a Forever stamp priced at $1.27 that covers the base First-Class rate plus the non-machinable surcharge for one ounce. Like other Forever stamps, it stays valid through future rate increases.5The Postal Store. Colorado Hairstreak Stamps $1.27 Buying a roll before you mail square invitations is the simplest way to handle postage without recalculating at the counter. If the letter weighs more than one ounce, you’ll also owe the standard additional-ounce rate on top.
What Happens If You Underpay
Drop a non-machinable letter in the mail with only a standard Forever stamp and USPS will catch the shortfall during processing. The usual outcome is that the letter comes back to you with a notice showing how much more postage is needed. Without a return address, USPS may deliver it “postage due,” meaning the recipient has to pay the difference to receive it.
Either way, the letter is delayed. For wedding invitations, bill payments, or anything else with a date attached, that delay can matter. Using the $1.27 Forever stamp or having a clerk price each piece before you send it avoids the problem entirely.
Hand Cancellation Is Not a Separate Fee
Because non-machinable letters can’t run through the machine canceler, USPS cancels the stamp by hand. The surcharge already covers this handling, so there’s no additional charge if you request hand cancellation at the counter for something like a wedding invitation where you want a clean postmark. Practices vary by location. Some clerks cancel the envelopes behind the counter, and some hand you an ink stamp to do it yourself, especially with a larger batch.