Originally Posted by dassie
In Calibre, select the book, then press convert. Move to the Look And Feel page of the conversion options, and select the ´filter style information´ tab. In the other CSS Properties field, enter `line-height`. Then press Ok.
In addition, you can set this as your default way to convert: go to Preferences > Conversion > Common Options. Calibre also allows you to do large-batch conversions quickly and easily.