Window Envelope Sizes: Dimensions and Placement Rules

A window envelope has a transparent panel — usually a thin film of cellophane or glassine — cut into the front of the envelope. When a billing statement or invoice is folded and inserted correctly, the recipient's address printed on the document shows through the window. No labels, no separate addressing pass, no printer time spent on envelopes.

This is the format that drives nearly all consumer billing in the United States: utility bills, credit card statements, insurance invoices, medical billing, and bank statements. The window envelope architecture is built around volume mailing efficiency.

This page covers the sizes window envelopes are available in (most commonly #10 and #9), single versus double-window varieties, USPS placement rules, and design considerations for billing-statement layouts.

When to use a window envelope

Invoices and statements

Single-window #10 envelopes are the dominant format for invoices, billing statements, and account summaries. The address prints in the upper-left of a folded statement; when the statement is trifolded with the address panel facing forward, it shows through the window in the lower-left of the envelope.

Double-window for account references

Double-window envelopes have two windows: the lower window shows the recipient address (same as single-window), and the upper window shows an account number, return-reply address, or transit-routing reference. Common in financial services and high-volume billing where the upper window helps with sortation or response handling.

Payroll and employee mailings

Window envelopes are common for paystubs (when paper checks are still mailed), W-2 forms, and HR correspondence. The format allows pre-printed forms to mail without manual addressing.

Government and insurance correspondence

Tax notices, benefits statements, insurance EOBs (explanations of benefits), and government program letters use window envelopes for the same reason commercial billing does: high volume, pre-printed addresses on the contents, no labeling step.

When not to use a window envelope

For personal correspondence, invitations, marketing letters where the envelope is meant to feel personal, or any mailing where the contents don't have the address pre-printed in the right position, a non-window envelope is the better choice.

Window envelope postage and USPS placement rules

2026 First-Class postage

Window envelopes follow standard letter-rate postage based on the underlying envelope size:

• #10 window envelope, 1 ounce: $0.78 Forever stamp / $0.74 metered
• #9 window envelope, 1 ounce: $0.78 / $0.74 metered
• Each additional ounce up to 3.5 oz: $0.29

The window itself doesn't change the postage class — windows made of paper-compatible material (cellophane, glassine, or polypropylene film under USPS specs) keep the piece in letter-rate territory.

USPS DMM 202 window placement rules

USPS regulates where windows can sit on the envelope to ensure address barcodes print correctly and read accurately on automation equipment. Key rules:

• Address must show fully through the window even if the contents shift up to 0.25 inches in any direction
• Clear space required around the address — no printed lines, logos, or graphics within the window or directly adjacent
• Window film must be transparent enough for OCR scanners to read printed addresses through it
• No reflective films — glossy or metallic windows interfere with USPS scanning equipment

Standard window dimensions and placement

Common #10 single-window placement: window approximately 4.5 inches wide by 1 inch high, positioned 0.5 inches from the bottom edge and 0.875 inches from the left edge. These specs vary slightly by manufacturer and use case — confirm the exact window position on your envelope stock matches the address position on your printed contents before running a production batch.

Last verified: May 2026. Source: USPS Domestic Mail Manual 202.