@WindowsXP
The forum signature CSS class that defines the dimensions is set to 686px wide and 102px tall. If you use columns, you lose about 10px between padding and margins.
The forum post CSS class is defined with a minimum height of 200px. This will vary on screen size. Mine has it at about 676px.
The "editable userpage space" CSS class is set to a maximum height of 600px. This will also vary on screen size. Mine is about 509px.
All catmojis are 35x35px.