Letter Size and Weight Guide
Postage depends on the completed mailpiece, not the sheet of paper alone. Seal the envelope, then measure and weigh it in the form that will actually be mailed.
Retail Letter Limits
| Dimension | Letter range |
|---|---|
| Length | At least 5 inches and no more than 11.5 inches |
| Height | At least 3.5 inches and no more than 6.125 inches |
| Thickness | At least 0.007 inch and no more than 0.25 inch |
| Weight | No more than 3.5 ounces for First-Class Mail letters |
Shape Can Change the Price
A letter can be within the basic size limits and still be nonmachinable because it is square, too rigid, uneven, closed with certain clasps, or addressed in an incompatible direction. Pieces outside letter standards may be priced as flats or packages.
Reliable Measurement
- Assemble and seal a representative piece.
- Use a ruler and a scale suitable for small increments.
- Check the thickest point and whether contents shift.
- Round weight according to the applicable price step.
- Confirm current rates before mailing the full batch.
Stamp Size Is a Separate Measurement
Envelope dimensions determine the mailpiece category, while the physical dimensions of the adhesive stamp are a different subject. Read the postage stamp size guide when you need to compare stamp dimensions, orientation, or package format.
After confirming that a mailpiece qualifies as a letter and calculating the amount due, compare postage stamps for qualifying letters.
Sources and Scope
The completed piece controls classification; dimensions alone do not establish machinability.