Regarding A, B and C ISO sizes, they aren't mysterious:<p>- the aspect ratio is square root of 2 to 1, so that cutting in half the long side leaves two sheets with the same aspect ratio.<p>- A is the main series, with A0 approximately one square meter.<p>- B sizes are square root of 2 times larger in area than A formats with the same numbers, filling the gaps.<p>- C sizes are slightly larger than A sizes, suitable for containers, envelopes etc. for them.
Now I'm confused. The article says at one point that ANSI "letter" is 8 1/2 inches by 12 2/3 inches and also that "letter" size is 8 1/2 inches by 11 inches without explaining the discrepancy. So which is it?