Envelopes

The International paper system specifies envelope sizes based on the A paper sizes.

For each A size there is a slightly larger “C” size for envelopes. Thus A4 paper fits neatly into a C4 envelope. A5 paper (or A4 folded in two) fits neatly into a C5 envelope.

An additional useful envelope size is the long-format “DL” envelope designed to accommodate A4 paper folded in three.