need help determining the partition size of working disks.

I am the lucky person to take over the maintenance of an existing RAID5 array. Recently I realized that sda was dead. Obviously I have to replace the disk with a new working one. The problem is, I need to partition the new disk before I can integrate it in the RAID5 volume. I believe that the partition on new disk has to be exactly the same as on others disks. But how do I find the partition information (size and type) on the other working disks?
Thanks in advance.