Envelope sizing

Envelope sizes are usually given in 'C' numbers. A C6 envelope fits a card blank that has been made by folding an A5 sheet of card to A6. If you are making your own card blanks, it is best to make them to a size that fits the most commonly found sizes of envelope as it may be hard for you to find other sizes.

The most common sizes:-
114 x 162mm (C6)
110 x 220mm (DL)
130 x 130mm (square)

Other common sizes:-
162 x 229mm (C5)
125 x 175mm
155 x 155mm (square)

A DL envelope is the size of a business envelope - it takes a sheet of A4 paper folded into 3. As there is no 'A' size card that corresponds with a card blank folded to fit in an envelope of this size, the card blanks are often referred to as DL as well.