A standard one-ounce non-machinable letter needs two Forever stamps. The postage due is $1.27, which comes from the $0.78 First-Class Mail base rate plus a $0.49 non-machinable surcharge, and two Forever stamps at $0.78 each give you $1.56 in postage. You’ll overpay by $0.29, but USPS doesn’t make change on stamps. If that bothers you, a single $1.27 non-machinable stamp covers the whole thing exactly.1USPS. Notice 123 – January 2026 Price List
Why the Surcharge Applies
USPS runs most letters through high-speed sorting equipment. When an envelope can’t ride those machines safely, a clerk has to handle it by hand, and that manual processing is what the $0.49 surcharge pays for.
Common triggers include:
- Square envelopes, and any envelope whose length-to-height ratio falls outside 1.3 to 2.5.
- Plastic wrapping or a non-paper exterior. Clear address windows on paper envelopes are fine.
- Clasps, string-and-button closures, metal brads, or similar fasteners.
- Lumpy contents like pens, keys, or coins that create uneven thickness.
- Envelopes too rigid to bend around the belts inside sorting machines.
- Pieces longer than 6 inches or taller than 4ΒΌ inches that are thinner than 0.009 inches.
- An address printed parallel to the short side of the envelope instead of the long side.
Self-mailers and booklets that don’t meet USPS preparation standards also qualify.2Postal Explorer. Domestic Mail Manual 101 Physical Standards for Retail Letters, Flats, and Parcels Wax seals aren’t spelled out in the rules, but they create uneven thickness and can act as a closure, so treating a wax-sealed envelope as non-machinable is the safer call.
The Exact-Postage Alternative
USPS sells a dedicated non-machinable stamp worth $1.27, which covers the base postage and the surcharge in a single stamp with nothing left over.1USPS. Notice 123 – January 2026 Price List Look for it on the USPS online store under the “Non-Machineable” category, or ask at the counter. If you send square greeting cards or wedding invitations regularly, keeping a book on hand is cheaper than paying two Forever stamps every time.
The other exact-postage route is a self-service kiosk at a post office, which prints labels down to the penny.
Heavier Non-Machinable Letters
If your letter weighs more than an ounce, each additional ounce (or part of one) adds $0.29 to the base rate before the surcharge. A First-Class letter can weigh up to 3.5 ounces; past that, it’s reclassified as a large envelope with different pricing.3USPS. First-Class Mail and Postage
Stamp counts by weight, using Forever stamps at $0.78 each:
- Up to 1 oz: $1.27 total, two Forever stamps.
- Over 1 oz to 2 oz: $1.56 total, two Forever stamps exactly.
- Over 2 oz to 3 oz: $1.85 total, three Forever stamps.
- Over 3 oz to 3.5 oz: $2.14 total, three Forever stamps.
The base rates for each tier come from the January 2026 price list.4USPS: Notice 123. Notice 123 – January 2026 Price Change A two-ounce non-machinable letter is the sweet spot: two Forever stamps cover it with zero waste. The July 2025 rates were confirmed to hold through at least early 2026.5USPS About. U.S. Postal Service Announces No Stamp Price Changes for January 2026
Non-Machinable Letters Going Abroad
The $0.49 surcharge applies to international First-Class Mail letters too.6Postal Explorer. Notice 123 – January 2026 Price List A Global Forever stamp covers $1.70 for a one-ounce international letter, so a non-machinable international letter costs $2.19.7USPS. 2026 Postage Price Change Three Forever stamps ($2.34) cover it, but if you’re mailing internationally often, buying exact postage at a kiosk or counter beats overpaying $0.15 each time.
What Happens If You Underpay
Missing the surcharge on a non-machinable letter is one of the more common postage mistakes, and USPS handles it differently than an ordinary shortpaid letter. A regular letter with too little postage usually goes to the recipient with a “postage due” notice. A non-machinable letter with too little postage gets returned to the sender for additional postage instead.8Postal Explorer. Domestic Mail Manual P011 Payment Your square wedding invitation doesn’t just arrive late with a fee; it comes back, and you have to add postage and resend.
If there’s no return address, the letter is treated as dead mail and generally ends up at the Mail Recovery Center. Writing “non-machinable” on the envelope when you know the surcharge applies helps postal workers route it correctly the first time.