Paper sizes.
A4 210 x 297mm.
The same size as a regular piece of office photocopy paper. Cut to your own specifications or use whole. Paper weight folds in half to fit into a C5 envelope, in three to fit into a DL (business sized) envelope, or in four to fit into a C6 envelope.
A4 is used a lot in Europe but little in North America
In Imperial measure it is:
8.2740 inches x 11.7018 inches
Thanks
Jason