Please do the following:

1) In the settings, go to "Business settings >> Volume units".
2) Either edit an existing unit or create a new one. In the lower half of the Edit window, select the "Words" button and enter how many words the unit will be equal to.

3) Go to "Advanced Settings >> CATCount", click the "Change" button, and select the new unit.

You will still need to enter the volumes in words in the CatCount window itself, but once you confirm the count, the "Volume" field in the "Edit job" window will display the final result in the new units.