USPS Envelope Size
An envelope can fit within USPS letter dimensions and still need extra postage if the address runs along the short edge.
When I saw the envelope making on the internet, I started to think about why I paid for envelopes for years. The same thing happens when I examine "how it works" channels on the Internet.
Buying is something I've tried before. I know how to buy it. Making a simple envelope is a small enough project to try at home.
Measure the envelope after you fill it
The size limits above apply to the sealed envelope. Measure its thickness at the fullest part. The limit is ¼ inch. The minimum is 0.007 inch, rising to 0.009 inch for machine processing if the envelope is over 6 inches long or over 4¼ inches high.
On a rectangular envelope, write the address along the long edge. USPS treats a letter addressed along the short edge as nonmachinable, even when it fits the size limits. A square envelope also falls outside the 1.3–2.5 length-to-height ratio for machine processing.
If your envelope exceeds any of the letter-size maximums, check the USPS rules for letters and flats before buying postage. To choose a format based on the paper you’re folding, see the business envelope dimensions.
