Envelope Sizes

Envelope Size Systems Around the World

There are four main envelope sizing systems in international business. Understanding which system a size belongs to helps you match an envelope to the sheet it carries — and to your customer's local conventions.

System	Region	Naming	Common Sizes
ISO C-series	Europe, Asia, most of the world	C4, C5, C6, DL — built to fit A-series paper	DL envelope dimensions 110 × 220 mm, C6 envelope dimensions 114 × 162 mm, C5 envelope dimensions 162 × 229 mm, C4 envelope dimensions 229 × 324 mm
ISO A-series	Worldwide (cards & invitations)	A2, A6, A7, A9 — announcement sizes	A6 105×148, A7 105×152 mm
US Commercial (#)	North America	#6¾, #7, #9, #10	#10 4⅛×9½ in (105×241 mm)
China National	China	No. 1 – No. 9	ZL 120 × 230 mm business standard

Envelope Sizes We Manufacture

Eleven standard sizes manufactured factory-direct. Dimensions are exact production sizes; click any envelope size for full specifications, paper stock and printing options.

Envelope Size	Dimensions (mm)	Dimensions (in)	Fits	Typical Use
DL envelopes	220 × 110	8.66 × 4.33	A4 folded in thirds	Standard European business correspondence
C5 envelopes	229 × 162	9.02 × 6.38	A5 flat, or A4 folded once	A5 documents, brochures
C6 envelopes	114 × 162	4.49 × 6.38	A6 flat, or A4 folded twice	Gift cards, small inserts, A6 postcards
C4 envelopes	324 × 229	12.76 × 9.02	A4 flat	Contracts, certificates, catalogs
B6 envelopes	176 × 125	6.93 × 4.92	A5 folded once	Small booklets, cards
B5 envelopes	176 × 250	6.93 × 9.84	A5 flat, or A4 folded once	Brochures, catalogs, booklets
B4 envelopes	250 × 353	9.84 × 13.90	A4 flat, or A3 folded once	Large documents, drawings, contracts
ZL envelopes	230 × 120	9.06 × 4.72	Business sheets folded	Standard Chinese business mail
#1 envelopes	165 × 100	6.50 × 3.94	Business cards	Cards, small notes
#2 envelopes	175 × 110	6.89 × 4.33	Cards, folded A6	Small invitations, invoices
#8 envelopes	250 × 162	9.84 × 6.38	A4 folded once	Documents, contracts

Need a different dimension? We cut custom envelope sizes to your exact specification — see custom envelope manufacturing.

Standard Envelope Size Chart — US, A-Series, Flat & Square

Beyond the eleven sizes we manufacture to order, these are the standard formats used across US and international mail. Dimensions are nominal industry sizes.

US Commercial (#) Envelope Sizes

Size	Dimensions (inches)	Fits	Typical Use
#6¾	3⅝ × 6½	Check, small statement	Personal correspondence
#7	3¾ × 6¾	Small form	Small forms, notes
#8⅝	3⅝ × 8⅝	Check, statement	Statements, checks
#9 envelope measurements	3⅞ × 8⅞	Fits inside #10	Reply envelopes
#10 envelope measurements	4⅛ × 9½	8½×11 folded in thirds	Standard business mail — invoices, statements, letters
#11	4½ × 10⅜	Larger correspondence	Larger business mail
#14	5 × 11½	Unfolded letter-size sheets	Legal documents

A-Series Envelope Sizes (Announcement)

Size	Dimensions (inches)	Fits Card Size	Best For
A2	4⅜ × 5¾	4¼ × 5½	RSVPs, gift notes, thank-you cards
A4	4¾ × 6½	4½ × 6¼	Small cards
A6 envelope size	4¾ × 6½	4½ × 6¼	Invitations, save-the-dates, 4×6 photos
A7 envelope size	5¼ × 7¼	5 × 7	Wedding invitations — most popular
A8	5½ × 8⅛	Larger invitation	Larger invitations
A9	5¾ × 8¾	5½ × 8½	Formal announcements
A10	6 × 9½	5¾ × 9¼	Oversized announcements, certificates

Large Flat & Catalog Envelope Sizes

Size	Dimensions (inches)	Fits	Best For
6×9 envelope size	6 × 9	A5 booklets, tri-fold brochures	Marketing mailers, small catalogs
9×11½	9 × 11½	Flat document	Flat mailings
9×12 envelope dimensions	9 × 12	8½×11 sheets flat	Catalogs, annual reports, legal docs
10×13 envelope dimensions	10 × 13	Oversized materials	Large catalogs, thick documents

Square & Specialty Envelope Sizes

Style	Dimensions (inches)	Best For
square envelope sizes	5 × 5	Party invitations, events, greeting cards, RSVP
square envelope sizes	5½ × 5½	Invitations
square envelope sizes	6 × 6	Formal invitations, photography mailers
Baronial	Various (pointed flap)	Formal invitations, social stationery
coin envelope sizes	2½×4 to 4×7	Donation envelopes, payment remittance

How to Choose the Right Envelope Size

Match the envelope to what you are mailing — three quick steps:

1. Measure the contents. A flat A4 sheet needs a C4; folded once it fits a C5; folded in thirds it fits a DL. A business card fits a #1.
2. Consider the purpose. Daily business mail → DL or #10. Invitations and greeting cards → A-series or #2. Contracts and legal documents → C4 or 9×12.
3. Check postage class. Sizes above letter limits are charged as flats or parcels — choosing the smallest envelope that fits keeps postage down.

What you are mailing	Recommended envelope size
A4 sheet, flat (contracts, certificates)	C4 envelope size 229 × 324 mm
A4 sheet, folded in thirds	DL envelope size 110 × 220 mm
A4 sheet, folded once	C5 envelope size 162 × 229 mm
A5 document or brochure	C5 envelope 162 × 229 mm
Business card or small note	#1 envelope 100 × 165 mm
Invitation card (4×6 photo / A6)	#2 or A6 — see envelopes for 4×6
Thick catalog or annual report	9×12 or 10×13 — see catalog envelope standards

Choosing by Insert Size

Match the envelope to what you're mailing:

Your insert	Envelope size
Letter, folded in thirds	#10 or DL envelopes
Letter, half-fold	6×9 or A10
5×7 card	A7
4×6 photo	A6
Flat 8½×11	9×12 or C4 envelopes
Check / short form	#6¾ or #9

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

Envelope Size and Postage Classes

Postal services classify mail by size, thickness and weight. The size of your envelope decides the rate class — which is why picking the smallest envelope that fits your contents saves money.

Postage class	Typical envelope sizes	Note
Letter	DL, #10, #1, #2	Lowest rate — the everyday business envelope range
Large letter / Flat	C5, B6, #8	Mid rate — larger but still machinable when flexible
Parcel	C4 and above (when rigid or thick)	Highest rate — stiff or thick items, or dimensions beyond flat limits

Rates and dimensional thresholds differ by postal service and change over time — check your local carrier before bulk mailing. Need guidance on a size that stays in the economical band? Ask us.

Paper Weight and Envelope Size

Larger envelopes need heavier paper to hold their shape through the mail. A floppy C4 in thin stock crumples in the sorting machine; a stiff DL in heavy card is unnecessary cost.

Envelope size	Suggested paper weight	Why
DL, #1, #2 (small)	80–120 g/m² woodfree or kraft	Light handling, low cost
C5, B6, ZL (medium)	120–200 g/m²	Good rigidity for inserted sheets
C4, #8 (large)	150–250 g/m²	Holds A4 documents flat without bending
All sizes, premium	Up to 350 g/m² art-coated	Invitations, luxury mail, photo envelopes

Full stock options — woodfree, kraft, coated, recycled and more — are covered in our envelope paper weight guide.

Envelope Sizes for Common Uses

Use case	Recommended size	Why
Daily business correspondence	DL or #10	Universal business standard, letter postage
Invoices and statements	DL with window, or #9 reply	Automated insertion — see billing envelopes
Wedding invitations	A7 / A6 or #2	Card-friendly formats — see wedding invitation envelopes
Contracts and legal documents	C4 or 9×12	A4 flat, tamper-evident options available
Catalogs and annual reports	9×12 / 10×13 open-end	See catalog envelope standards
Marketing and direct mail	DL, #10 or custom	Branded outer — see business envelopes with logo

Custom Envelope Sizes — When Standard Doesn't Fit

If your insert doesn't match any standard size — or you're designing packaging that needs a unique format — custom envelope manufacturing is the answer. We produce envelopes in any dimension with custom die-cut windows, specialty papers, and your choice of printing and finishes.

Custom sizes typically require a minimum order of 2,000 pieces to cover die fabrication costs. For standard-size envelopes with custom printing, MOQ drops to 1,000 pieces.

Envelope Size FAQ

Explore Each Envelope Size

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