Standard Letter Envelope Size In Inches. A standard letter envelope must be no smaller than 3 1/2 inches by 4 inches and no larger than 6 1/8 inches by 11 1/2 inches, according to postal regulations. Nearly all businesses need #10 envelopes, which measure 4 1/8” by 9 1/2 “ and hold a standard sheet of paper folded in thirds.
Ideal for mailing greeting cards, regular letters and postcards, the maximum size that would fall under a 'letter' is 165 mm x 240 mm. Browse letter+size+envelope on sale, by desired features, or by customer ratings. These envelopes are the perfect choice when mailing items too thick to fit in a standard envelope, like books, financial reports, and gifts!
We would recommend using an envelope no larger than c5 to fit these restrictions comfortably and avoid any excess costs.
Envelopes come in many styles and formats to complement a wide variety of paper types,. While the c5 envelope size can comfortably fit an a4 paper folded. This is the type of envelope typically used for business correspondence, and it probably makes up the majority of mail you receive. Folder expansion (inches) folder or paper size.