How to calculate the subnet mask when the IP address and the number of computers to address is given?

Question

Example:

IP: 140.140.0.0 Computers: 2046

Mask = ? And subnets = ?

Answer 1

To address 2046 hosts you need 11 bits (2^11 = 2048) so the smallest subnet you can have needs subnet mask of /21 (255.255.248.0). Your IP belongs to class B network which has 16 bit network mask so you have 21-16=5 subnet bits which gives you the number of subnets — 2^5 = 32.