#10 Envelopes

The #10 envelope is the standard business envelope in the United States. Every standard letter, invoice, statement, and piece of formal correspondence that gets folded and mailed goes in a #10. It's the format accounting software is built around, the size postal automation equipment is calibrated for, and the envelope that every office already knows. At Business Envelopes, we carry the full #10 lineup: plain white, tinted security, window, self-seal, colored wove, starburst, and double window formats, all available blank or with custom logo and return address printing. Free shipping on every order with no minimums.

What Is a Number 10 Envelope?

A #10 envelope measures 4 1/8 inches tall by 9 1/2 inches wide (4.125 x 9.5 inches). It holds a standard 8.5 x 11 sheet of paper folded into thirds, which is how virtually every business letter, invoice, and statement is prepared for mailing. The folded panel sits inside the envelope with roughly an eighth of an inch of clearance on each side, which is the tolerance that allows machine insertion to work cleanly at speed.

The "#10" designation comes from a commercial envelope classification system standardized in the 1870s. It has nothing to do with the envelope's dimensions and everything to do with the numbering scheme that brought consistency to an industry that previously had no standards. What matters now is that the 4 1/8 x 9 1/2 inch format qualifies for USPS First-Class letter-rate postage when contents are under 3.5 oz, and that it's compatible with every automated mail processing system the postal service runs. Non-standard sizes that fall outside the letter-rate window get reclassified as flats or trigger surcharges. The #10 clears the letter-rate threshold cleanly on both height and length.

#10 Envelope Size: Every Style We Carry

#10 White Envelopes, Gum Flap

Plain white 24 lb wove stock with a moistenable gum flap. The default for everyday business correspondence, available blank or with custom printing. Laser and inkjet compatible. Diagonal seam construction, V-shaped flap.

#10 Tinted White, Gum Flap

Same plain format with a security tint interior pattern that blocks document contents from showing through when the envelope is held up to light. Right choice for financial statements, medical correspondence, payroll, and any mailing where the contents carry sensitive personal or financial data.

#10 Tinted White, Peel and Seal

Security tint interior with peel-and-seal closure. No moisture required. The protected liner prevents pre-activation in storage, and the adhesive bonds on contact once the liner is peeled. Better fit than flip-and-stick when envelopes are stocked before a mailing run rather than processed immediately.

#10 Tinted Self Seal, Flip and Stick

Security tint with a flip-and-stick closure for faster per-piece sealing on high-volume runs. No liner to remove. Fold the tab up, press the flap down, sealed. Used by billing departments, insurance offices, and any operation running statement batches where sealing speed on each piece matters.

#10 Window Envelope, Gum Flap

Clear poly-film window at the standard left position (1 1/8 x 4 1/2 inches, 7/8 inch from left, 1/2 inch from bottom) aligns with standard invoice and letter address blocks from QuickBooks, Xero, FreshBooks, and all standard templates. Recipient's address shows through from the document. No labeling or envelope addressing needed.

#10 Window Tinted, Gum Flap

Window format with security tint interior. The window shows the address, the tinted body blocks everything else from view. Standard choice for billing departments sending invoices with account numbers or financial data visible on the document face.

#10 Window Tinted, Self Seal

The most commonly ordered format in this category for high-volume operations. Window for address display, tinted interior for document privacy, flip-and-stick closure for fast moisture-free sealing on billing runs. Available with custom logo and return address printing.

Double Window #10 for Invoices and Statements

Two windows instead of one. Top window shows your return address from the document, bottom window shows the recipient address. Eliminates all addressing work on both sides of the envelope. Used for invoices, statements, and any recurring correspondence where both address fields come from the printed document.

#10 Wove Colored Envelopes

Available in a range of wove colors for mailings where visual presentation matters before the envelope is opened. Used by membership organizations, professional services, and direct mail programs that need to stand out in a mail pile. Custom printing available on all colors.

#10 Starburst Envelopes

Bold starburst color pattern on the envelope face. Peel-and-seal closure. Designed for fundraiser mailers, direct mail campaigns, and any mailing where open rate depends on the envelope catching attention before anything else.

Size 10 Envelope: Dimensions, Capacity, and USPS Compliance

The standard #10 envelope size of 4 1/8 x 9 1/2 inches sits comfortably within USPS letter-rate dimensions, which run from 3.5 x 5 inches up to 6.125 x 11.5 inches. Pieces within that range, under a quarter inch thick and under 3.5 oz, process at First-Class letter postage. Pieces outside that range get reclassified at higher flat-mail or non-machinable rates. The #10 handles standard letter content cleanly at letter-rate without any adjustments.

Interior capacity runs 4 x 9.25 inches. A standard 8.5 x 11 sheet folded into thirds produces a panel roughly 3.67 x 8.5 inches, which fits with clearance on all sides. That clearance is intentional. Too tight and the sheet jams during machine insertion. Too loose and the contents shift visibly. The #10 format is calibrated to the way business letters are actually folded and inserted, not just to the outer dimensions of the paper.

What Is the No 10 Envelope Size in Other Units?

For designers, print vendors, or anyone working across measurement systems: the #10 envelope measures 105 x 241 mm in metric, or approximately 10.5 x 24.1 cm. The interior workspace is 101.6 x 234.95 mm. These are the dimensions to use when setting up artwork in design software or coordinating with an international print vendor. The USPS standard is expressed in inches, but both metric values describe the same envelope.

Custom Printing on #10 Envelopes

Every #10 style in this lineup supports custom printing. Return address, company name, logo, tagline, mailing indicia, all printed directly on the stock before the envelopes ship. Blank stock ships same or next day. Custom printed orders ship in 7 to 10 business days from proof approval. Artwork stays on file for reorders. For volume programs across multiple #10 styles, request a bulk quote here. For other envelope sizes that work alongside #10s in a complete mailing program, browse our full size catalog or check our window envelopes and double window envelopes categories.

Frequently Asked Questions About #10 Envelopes