Professional #10 Envelopes

A #10 envelope measures 4⅛ inches wide by 9½ inches tall (4.125" x 9.5"), making it the standard business envelope size in the United States. It's designed to hold standard 8½" x 11" letter paper folded in thirds (trifold style). The envelope's rectangular shape qualifies for USPS letter-rate postage when under 3.5 ounces.

Fold standard 8½" x 11" paper into thirds to fit perfectly in a #10 envelope. Place the letter face-up, fold the bottom third up, then fold the top third down to create a trifold (also called 'hot dog style'). The folded document will measure approximately 3⅔" x 8½" and slide easily into the envelope. For professional mailings, ensure text begins at least ½ inch from top of the page to avoid folding through important information.

A #10 envelope with up to 4 sheets of standard 20lb paper requires one Forever stamp (currently $0.68 in 2025) for First-Class Mail delivery. Each additional ounce costs $0.28 extra, up to a maximum of 3.5 ounces for letter-rate postage. An empty #10 envelope weighs approximately 6.75 grams, so calculate your contents accordingly. Envelopes over 3.5 ounces are classified as 'flats' with different pricing.

#10 envelopes (4⅛" x 9½") are the standard business size for 8½" x 11" letters folded in thirds. #9 envelopes (3⅞" x 8⅞") are smaller and commonly used as return envelopes that fit inside #10s, or for smaller documents like invoice stubs and payment remittance forms. If you're mailing standard business correspondence, #10 is your default choice; use #9 for reply envelopes or smaller contents.

You can fit approximately 4-5 sheets of standard 20lb paper in a #10 envelope and stay under the 1-ounce limit for a single Forever stamp. The envelope itself weighs about 0.24 ounces, leaving 0.76 ounces for contents. Each sheet of standard copy paper weighs approximately 0.16 ounces, so 4 sheets plus envelope equals roughly 0.88 ounces. For thicker paper stock, cardstock inserts, or multiple enclosures, weigh your assembled mailing to calculate accurate postage.

#10 envelopes are the industry standard for business correspondence including letters, invoices, statements, bills, and checks. Their size accommodates standard 8½" x 11" documents folded in thirds, making them ideal for both personal and professional mailing. Common uses include monthly billing statements, payroll checks, tax documents, direct mail marketing, and everyday business letters.

Choose window envelopes for high-volume mailings with pre-printed addresses (invoices, statements, bills) to save time and reduce addressing errors. Choose windowless envelopes for personalized correspondence, confidential mailings requiring privacy, or creative designs needing the full printable surface. Window envelopes work best with automated insertion equipment and accounting software like QuickBooks.

Security tinted envelopes feature an internal pattern (usually blue, black, or gray) that obscures contents and prevents read-through of sensitive information. Use security tint for financial documents, checks, confidential business correspondence, or any mailing containing private data. Standard envelopes without security tint are more economical and suitable for non-confidential general correspondence, marketing materials, and everyday business letters.

Gummed (moistenable) seals are most economical and work best with automated mail machines for high-volume operations, but require water or a moistener to activate. Self-seal (peel & stick) envelopes have an adhesive strip under a protective liner—no moisture needed—ideal for manual preparation and office use, though slightly more expensive. Gummed envelopes have unlimited shelf life; self-seal types last 12-18 months. Choose based on volume (high = gummed) and preparation method (manual = self-seal).

Yes, most #10 envelopes work with both laser and inkjet printers, though you should verify your printer's specifications. Most modern printers include a manual feed slot or envelope tray setting. For best results, use envelopes specifically labeled 'laser safe' or 'inkjet compatible,' adjust your printer settings to 'envelope' mode, and test with a single envelope first. We also offer custom pre-printed options with your logo, return address, and branding for larger orders.

24lb paper is the industry standard for business envelopes, offering good durability and professional appearance at reasonable cost. Choose 20lb (economy weight) for high-volume, budget-conscious mailings like mass marketing. Choose 28lb or heavier for premium feel in executive correspondence, professional services, or upscale marketing. Paper weight doesn't significantly affect postage until you reach very heavy stock with multiple enclosures.