The text area in Joomla Article Edit can be made larger by dragging the bottom right corner, but it can also be set to open at a specific size.
For TinyMCE (the default text editor):
Go to
Extensions -> Plugin Manager -> Editor - TinyMCE
In the Advanced Parameters of TinyMCE enter values for "HTML Height" and "HTML Width"
Typical values would be 1000 and 550 respectively.
For JCE text editor:
JCE is an enhanced controller for TinyMCE.
It has Profiles which (among other things) enables the text area to be set at various sizes depending on User Group.
The size of the text area can be set for each Profile.
Components -> JCE Administration -> Profiles [Default profile]
"Editor Width" and "Editor Height" are in the "Editor Parameters" tab.
