A square letter is nonmachinable because its aspect ratio is below the machinable-letter threshold. Under the USPS retail schedule effective July 12, 2026, a qualifying square letter pays the applicable First-Class letter postage plus a $0.49 nonmachinable surcharge.
Current stamped-letter examples
| Completed weight | Letter postage | Square/nonmachinable surcharge | Total |
|---|---|---|---|
| Up to 1 oz | $0.82 | $0.49 | $1.31 |
| Over 1 oz up to 2 oz | $1.11 | $0.49 | $1.60 |
| Over 2 oz up to 3 oz | $1.40 | $0.49 | $1.89 |
| Over 3 oz up to 3.5 oz | $1.69 | $0.49 | $2.18 |
Why square mail is nonmachinable
Machinable letters need a rectangular proportion. USPS expresses this as aspect ratio—length divided by height. A square piece has a ratio of 1.0, below the machinable range, so it needs separate handling and the surcharge.
Before you add stamps
- Seal and assemble the final envelope, including cards and inserts.
- Measure length, height and thickness, then weigh it.
- Check rigidity, clasps, buttons, uneven thickness and other nonmachinable features.
- Confirm it remains within letter dimensions and the 3.5-ounce maximum.
- If it exceeds a letter boundary, price it as the correct mail class instead of merely adding the square surcharge.
Related guides
Sources and verification
Facts on this page were checked on August 31, 2026. Dynamic inventory, prices and USPS rules can change.
Explore the complete topic
This page covers one focused task. Return to usps non machinable stamp to compare the related pages, products, tools and reference material in this topic.