This international paper size reference covers ISO A-series dimensions, US sizes, and envelope sizes — with a paper folding guide showing which paper fits in which envelope. Essential for international mailing, printing, and design work.
How to Use the International Paper Size Reference
Use the tabs above to explore A-series dimensions, envelope sizes, and the folding guide. The folding guide is especially useful when preparing international correspondence — matching paper to envelope size prevents documents from not fitting or arriving damaged.
The A-Series Logic
ISO A-series paper maintains a consistent 1:√2 aspect ratio (approximately 1:1.414). This means you can fold any A-size in half to get the next smaller size with the same proportions. A0 has exactly 1 square meter of area. Each size down is half the area: A1 = 0.5m², A2 = 0.25m², A3 = 0.125m², A4 = 0.0625m². This makes scaling artwork and documents between sizes exact with no distortion.
C-Series Envelopes
C-series envelopes are specifically designed to hold A-series paper. The relationship is simple: C4 holds unfolded A4, C5 holds A4 folded once (equals A5 size), C6 holds A4 folded twice (equals A6 size). DL (110×220mm) holds A4 folded in thirds — this is the most common business envelope worldwide.
US vs International Usage
When printing documents for international use, always export as PDF with the page size set to A4 (210×297mm). US Letter documents open and print correctly on US machines but may get cut off when printed on A4 paper internationally. PDF preserves exact page dimensions regardless of printer paper size.
Frequently Asked Questions
Is this paper size reference free?
Yes, completely free with no signup required.
Is my data safe when using this tool?
Yes. This reference runs entirely in your browser. No data is sent to any server.
What envelope fits an A4 letter?
A4 (210×297mm) folded in thirds (accordion fold) fits in a DL envelope (110×220mm). A4 folded in half fits in a C5 envelope (162×229mm). Unfolded A4 fits in a C4 envelope (229×324mm).
What is the difference between C4 and A4 envelopes?
C4 is an envelope, not a paper size. A C4 envelope (229×324mm) holds an unfolded A4 sheet of paper. The C-series envelopes are designed specifically to hold A-series paper — C4 holds A4, C5 holds A4 folded once (= A5), C6 holds A4 folded twice (= A6).
What is a DL envelope?
DL (Dimension Lengthwise, or 'DIN Lang') is 110×220mm — the most common business envelope internationally. It holds an A4 letter folded into thirds. DL is what you see as the standard #10-equivalent envelope in European and international business correspondence.
Why is A4 used everywhere except the US?
A4 is the ISO 216 international standard, adopted by almost every country. The US and Canada use Letter (8.5×11 inches) which predates the ISO standard. The ISO A-series was designed so each size is exactly half the area of the one above it, with a consistent 1:√2 aspect ratio.