The standard envelope will be a US version Size #10 envelope. This is in the size of 10.4775 cm x 24.13 cm. This is intended to send mail off in a uniformed manner – however some documents mailed will be mailed in a not standard envelope. In this case, there might be an extra charge for not using standard envelopes. This is because the system is designed to work best with standard envelopes. For most correspondences, the #10 envelope is sufficient.