If you intend to mail statements that are folded and printed on regular size paper (8.5x11), then the appropriate envelope size is 4.1/8 x 9.1/2. However, if you prefer to send them unfolded, you should use a Manila envelope (9x12). Nonetheless, I observed that the remit-to address on the printed statements is somewhat centered ( See attachement), which may not be visible if windowed envelopes are used.
In this scenario, a viable solution would be to pre-print the remit-to address on a batch of envelopes and utilize windowed envelopes, positioning the customer address in the bottom left corner for visibility.
