What is the most common envelope size in the US?

The #10 envelope (4.125 × 9.5 inches / 105 × 241 mm) is the standard US business envelope. It holds a letter-size sheet folded in thirds and is used for most invoices, statements, and business correspondence.

What is the difference between A2 and A6 envelopes?

These are US announcement envelope sizes, not ISO A-paper sizes. A2 (4.375 × 5.75 in) fits a 4.25 × 5.5 in card — common for RSVPs and small notes. A6 (4.75 × 6.5 in) fits a standard A6 card (4.5 × 6.25 in) — popular for invitations and greeting cards.

What does DL stand for and what fits in it?

DL stands for "Dimension Lengthwise" (110 × 220 mm / 4.33 × 8.66 in). It is the standard European business envelope and holds an A4 sheet folded in thirds (or a C5 sheet folded in half). DL is the most widely used envelope format outside North America.

How do ISO C-series envelopes relate to ISO A-series paper?

ISO C-series envelopes are designed to hold the corresponding ISO A-series paper. C4 holds an A4 sheet flat. C5 holds an A4 sheet folded once (or A5 flat). C6 holds an A4 sheet folded twice (or A5 folded once). Each C size is slightly larger than the matching A sheet to allow for easy insertion.

What envelope fits a standard greeting card?

It depends on the card size. A 5 × 7 inch card typically uses an A7 envelope (5.25 × 7.25 in). A 4.25 × 5.5 in card uses an A2 envelope. A 4.5 × 6.25 in card uses an A6 envelope. Always choose an envelope at least 0.25 in larger than the card on each dimension.

What is the difference between a #9 and a #10 envelope?

A #9 envelope (3.875 × 8.875 in) fits inside a #10 envelope, making it ideal as a reply envelope. It is commonly used in direct mail packages where the recipient returns the #9 in the outer #10.

Envelope Size Reference

Name: Envelope Size Reference
Availability: InStock
Author: Nham Vu

Look up dimensions for every standard envelope — US, European ISO, and international formats — with paper fit guidance in both inches and millimeters.

Name	Width	Height	Paper Fit	Common Use

Dimensions copied!

Summary

Look up dimensions for every standard envelope — US, European ISO, and international formats — with paper fit guidance in both inches and millimeters.

How it works

Select a format group (All, US Commercial, US Announcement, ISO C-series, or International) using the tabs.
Use the search box to filter by envelope name, paper fit, or keyword.
Toggle between inches and millimeters with the unit switch.
Click any row to expand details about paper fit and common uses.
Use the "Copy" button on a row to copy that envelope's dimensions to the clipboard.

Use cases

Choose the right envelope for a standard letter, invoice, or greeting card.
Verify that a folded paper or printed piece will fit a specific envelope.
Select ISO C-series envelopes for international shipping and business mail.
Find DL envelope dimensions for tri-fold A4 letters common in European correspondence.
Determine the correct envelope for wedding invitations, announcements, or marketing inserts.
Convert envelope dimensions between inches and millimeters for print setup.
Compare envelope sizes side by side when specifying print-and-mail jobs.
Identify the US commercial envelope equivalent for a given ISO C format.

Frequently Asked Questions

Last updated: 2026-07-15 · Reviewed by Nham Vu