If you are confused by the terminology, and don’t quite get the difference between A5 and C5, then this simple envelope size guide will hopefully explain everything.
An explanation of standard envelope sizes from C4 to C7
What do the A and the C mean?
Envelopes and paper have their own measurement system and at first it can seem a little baffling. It is actually quite simple, although I’ll admit it doesn’t help itself to make it easy!
Remember – A stands for paper and C stands for envelopes. Easy, right?
Starting with paper, A0 is actually 1 sqm. Yes, very metric. A1 is a sheet of A0 folded in half. A2 is half of A1 and so on down the line.
Envelopes sizes are listed under the prefix of ‘C’. Why remains a mystery but it really doesn’t matter. All you need to know is that envelopes are defined by a ‘C’ size and this corresponds to an equivalent ‘A’ paper size. The C size is a bit larger to accommodate the insert.
So that means that a flat sheet of A4 paper will require a C4 envelope if you don’t want to fold it. An A5 sheet will require a C5 envelope, and so on down.