RAID 5 cost in bytes.

Hi all. 
lets say i have 4 disks of 2TB each. configured in RAID 5 on the R310/R510 PERC7 controller.
so in the raid config i see 1862.50 X 4 disks.
How much space the raid controller is taking from each disk ?

in the end i have free storage 3 X 1862.50 ? (1 is off for RAID..) - 5587 GB ?

And if i will expand the raid with a fifth disk. it will expand my hardisk size to 5587+1862.50 ? 

thanks