How to define a new envelope size

I would like to define an envelope size for #6 3/4 envelopes. I know I can print them using a user-defined envelope size, but I actually want to add a size to the list of predefined sizes. Is that possible?

Please what is your LibreOffice version?

I’m running LibreOffice
Build ID: 350m1(Build:2
under Ubuntu 12.04

In the current version of LibreOffice,, the #6 3/4 envelope size is included in the list of envelope sizes. When this question was asked in 2014, the current version at the time may not have included it. But no, I don’t think it’s possible to add an envelope size to the list other than using the user-defined option.