A9 Envelope Size: Dimensions and Use Cases

The A9 envelope measures 5.75 inches high by 8.75 inches long. It sits at the upper end of the A-series and is the right choice when an A7 is too small but a 9×12 flat is overkill.

The A9 fits the half-page format — 5.5 by 8.5 inch cards, brochures, and programs — with a comfortable margin. It also accommodates 8.5 by 11 inch sheets folded in half lengthwise (folded to 5.5 by 8.5), which makes it useful for direct mail brochures and event programs.

This page covers exact dimensions, common use cases, USPS rules, and how the A9 compares to the smaller A7 and the larger A10.

When to use an A9 envelope

Larger formal invitations

Galas, charity benefits, and formal corporate events often use 5.5 by 8.5 inch invitation cards or fold-out invitation suites that exceed the A7 size. The A9 holds these without forcing a fold.

Wedding programs and event programs

Half-page programs handed out at ceremonies are often distributed pre-mailed in A9 envelopes for save-the-date packets, welcome kits, or informational mailings to out-of-town guests.

Direct mail brochures

An 8.5 by 11 inch brochure folded in half lengthwise (to 5.5 by 8.5) fits cleanly in an A9. This is a common format for premium direct mail pieces from financial services, real estate, and luxury brands — formats where the unfolded experience matters and a trifolded #10 mailing won't read as substantial.

Half-page booklets and magazines

Small-format publications and newsletters published at 5.5 by 8.5 inches mail in A9 envelopes when they're saddle-stitched and thin enough to qualify for letter rates.

When to step up or down

For a 5 by 7 invitation, drop to A7. For an unfolded 8.5 by 11 document or anything thicker than 0.25 inches, move to 9×12 flat.

A9 envelope postage and USPS rules

The A9 falls within USPS letter-size limits and qualifies for First-Class letter postage.

2026 First-Class postage for an A9 envelope

• 1 ounce, Forever stamp: $0.78
• 1 ounce, metered postage: $0.74
• Each additional ounce, up to 3.5 ounces: $0.29

The A9's aspect ratio is 1.52, well inside the machinable range of 1.3 to 2.5. The piece qualifies for automation as long as it's flexible, uniformly thick, and under 0.25 inches.

Weight watch

A9 mailings often hit the 2-ounce or 3-ounce tier because the contents — folded brochures, multi-page programs, premium cardstock — are heavier than typical letter-rate pieces. A 2-ounce A9 costs $1.07 (Forever stamp + additional ounce). At 3 ounces, it's $1.36. Run a full weight test on a finished sample piece before purchasing postage in bulk.

Last verified: May 2026. Source: USPS Domestic Mail Manual 201.