List of Envelope Sizes: Complete Dimensions & Size Chart

Introduction

There are dozens of envelope sizes, each sized to a specific insert — a letter folded in thirds, an invitation, a flat document, a small reply card. This is a complete list of envelope sizes with dimensions, so you can match any insert to the right envelope at a glance.

The list is organized by family — commercial (#10, #9, #6¾), A-series (invitations), large flats (9×12, 10×13), and square formats — with a note on what each one fits. For the full printable chart, see our envelope size chart.

Commercial Envelope Sizes

Commercial envelopes are the business standard, sized to folded letter paper.

#10 is the standard business envelope; #9 is its reply companion. For #10 in depth, see our number 10 envelope standards guide.

A-Series Envelope Sizes

The A-series is the invitation and stationery family, keyed to card sizes.

A7 is the most common invitation size; A6 fits a 4×6 photo. For invitation sizes, see our invitation envelope sizes guide.

Large Flat Envelope Sizes

Large flats carry documents without folding.

9×12 is the standard flat-document envelope. For 9×12 specs, see our 9×12 envelope standards guide.

Square Envelope Sizes

Square envelopes are the invitation-world signature, though they carry a postal surcharge.

For square sizes and the surcharge, see our square envelope sizes guide.

Choosing by Insert Size

Match the envelope to what you’re mailing:

The rule is simple: the envelope should be slightly larger than the insert, with room to slide in without forcing.

Conclusion

This list of envelope sizes covers the main families — commercial (#10/#9/#6¾), A-series (A2–A10), large flats (9×12/10×13), and square (5×5/6×6). Match the envelope to the insert, and use the full envelope size chart for a printable reference. For any size at production volume, request a quote.