ENVELOPE SIZES — FACTORY DIRECT

Envelope Sizes

A complete envelope size guide covering the ISO C-series, A-series and US commercial sizes — with exact dimensions in millimetres and inches, what fits inside each one, and how to choose the right envelope for business mail, invitations, documents and catalogs.

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 220×110, C6 114×162, C5 162×229, C4 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 230×120 mm business standard

Envelope Sizes We Manufacture

Eight 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
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
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.

How to Choose the Right Envelope Size

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

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.
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.
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 324×229 mm
A4 sheet, folded in thirds	DL envelope 220×110 mm
A4 sheet, folded once	C5 envelope 229×162 mm
A5 document or brochure	C5 envelope 229×162 mm
Business card or small note	#1 envelope 165×100 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

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

Envelope Size FAQ

What is the standard business envelope size?

In Europe and most of Asia the DL envelope (220×110 mm) is the business standard; in North America it is the #10 (4⅛ × 9½ in / 105×241 mm). See our standard business envelope size guide.

What size is a DL envelope?

A DL envelope is 220 × 110 mm (8.66 × 4.33 in) — sized for A4 paper folded in thirds. DL envelope details →

What is the difference between DL and C5 envelopes?

DL is long and slim (220×110 mm, for A4 folded in thirds). C5 is larger and squarer (229×162 mm) — it takes A4 folded once or A5 flat. C5 envelope details →

What envelope size fits an A4 sheet without folding?

A C4 envelope (324×229 mm) holds an unfolded A4 sheet. C4 envelope details →

What is a #10 envelope size?

A #10 envelope measures 4⅛ × 9½ inches (105 × 241 mm) — the US business standard for letterhead. #10 size standards →

What envelope size should I use for invitations?

A6 (105×148 mm) and A7 (105×152 mm) suit most invitation cards; square 5×5 and 6×6 formats are popular for premium invitations. See invitation envelope size guide.