61, that would all depend on what your building; inter walls, doors, windows, etc....
Lay your sill plate down next to your first top plate and lay them out togeather. What ever center you use, 24, 16, 12, is just that, the center of the stud so take off or add 3/4"- 1 1/2 in half is 3/4. On two of your walls you will have to burn 3 1/2" +3/4" bucause they will be inside of the first two walls.
Hope this helps ya, D.