How big would a reasonable sized study be?

[Karbea]

hello,

We are going to create a study out of the L bit of our lounge in our new house. Creating a rectangular lounge and study.
The room is currently 25'7x17'10max.
So the lounge is going to be 17'10 x ??? And the study about 12 x ??? What do you think would be reasonable room sizes for the new two rooms?

Thanks.