European (ISO) paper & envelope sizes

	millimetre	inch*	folds in	envelope
A3:	297 × 420	11¾ × 16½	quarters	to fit C5
			half	to fit C4 †
A4:	297 × 210	11¾ × 8¼	quarters	to fit C6
			thirds	to fit DL
			half	to fit C5
			unfolded	to fit C4 †
A5:	210 × 148	8¼ × 5¾	half	to fit C6
			unfolded	to fit C5
A6:	105 × 148	6 × 4	unfolded	to fit C6

* inch sizes approximate
† C4 size = Large Letter postage rate

envelope sizes

	millimetre	inch*
C6:	114 × 162 ‡	4½ × 6½
DL:	110 × 220	4¼ × 8¾
7 x 5:	134 × 184	5¼ × 7¼
C5:	162 × 229	6½ × 9
C4 †:	229 × 324	9 × 12¾

* inch sizes approximate
† C4 size = Large Letter postage rate
‡ some papers 111 x 159

envelope styles

banker - half-diamond shape flap opens on long edge (greetings card style)

pocket - parallel flap opens on short edge

wallet - parallel (or occasionally shallow diamond) flap opens on long edge

Please note that the exact shape of the envelope opening varies between ranges and between sizes within some ranges.