If you need to calculate subnet under Linux use an IP Netmask/broadcast calculator called ipcal. You can calculate IPv4 or IPv6 address. Supported features:

=> Multiple address and netmask input formats.
=> Retrieving of address information from interfaces.
=> Classfull and CIDR output.
=> Multiple address and netmask output formats (dotted quad, hex, number of bits).
=> Output of broadcast address, network class, Cisco wildcard, hosts/range, network range.
=> Output of multiple types of bitmaps.

=> Output of a user-defined number of extra networks.
=> Multiple networks input from commandline.
=> DNS resolutions of hostnames.
=> Compressed and expanded input addresses.
=> Compressed and expanded output.

=> Standard IPv6 network output.
=> v4 in v6 output.
=> Reverse dns address generation.
=> The ability to “split” a network based on a smaller netmask, also with recursive runs on the generated subnets.

[a] ipcalc : ipcalc takes an IP address and netmask and calculates the resulting broadcast, network, Cisco wildcard mask, and host range. By giving a second netmask, you can design sub- and supernetworks. It is also intended to be a teaching tool and presents the results as easy to understand binary values.

[b] sipcalc : Sipcalc is also an ip subnet calculator consisting of two parts. A plain text based console version, and web (cgi) based counterpart. Sipcalc, in it’s simplest form takes an ip-address and a subnet mask on the commandline and outputs information about the subnet. Sipcalc has support for both IPv4 and IPv6 addresses.

Install sipcalc and ipcalc

Use apt-get command:
$ sudo apt-get install sipcalc ipcalc
Please note that ipcalc is installed by default under RHEL / CentOS / Fedora Linux using initscripts package.

Examples

Let us see how to calculate subnets for 192.168.0.1/24:
$ ipcalc 192.168.0.1/24
Output:

Address:   192.168.0.1          11000000.10101000.00000000. 00000001
Netmask:   255.255.255.0 = 24   11111111.11111111.11111111. 00000000
Wildcard:  0.0.0.255            00000000.00000000.00000000. 11111111
=>
Network:   192.168.0.0/24       11000000.10101000.00000000. 00000000
HostMin:   192.168.0.1          11000000.10101000.00000000. 00000001
HostMax:   192.168.0.254        11000000.10101000.00000000. 11111110
Broadcast: 192.168.0.255        11000000.10101000.00000000. 11111111
Hosts/Net: 254                   Class C, Private Internet

You can also try sipcalc:
$ sipcalc 192.168.0.1/24
Output:

-[ipv4 : 192.168.0.1/24] - 0

[CIDR]
Host address            - 192.168.0.1
Host address (decimal)  - 3232235521
Host address (hex)      - C0A80001
Network address         - 192.168.0.0
Network mask            - 255.255.255.0
Network mask (bits)     - 24
Network mask (hex)      - FFFFFF00
Broadcast address       - 192.168.0.255
Cisco wildcard          - 0.0.0.255
Addresses in network    - 256
Network range           - 192.168.0.0 - 192.168.0.255
Usable range            - 192.168.0.1 - 192.168.0.254

More examples:

$ sipcalc 192.168.0.1 255.255.128.0 255.255.192.0
Output:

-[ipv4 : 192.168.0.1 255.255.128.0] - 0

[CIDR]
Host address            - 192.168.0.1
Host address (decimal)  - 3232235521
Host address (hex)      - C0A80001
Network address         - 192.168.0.0
Network mask            - 255.255.128.0
Network mask (bits)     - 17
Network mask (hex)      - FFFF8000
Broadcast address       - 192.168.127.255
Cisco wildcard          - 0.0.127.255
Addresses in network    - 32768
Network range           - 192.168.0.0 - 192.168.127.255
Usable range            - 192.168.0.1 - 192.168.127.254

-
-[ipv4 : 255.255.192.0] - 0

[CIDR]
Host address            - 255.255.192.0
Host address (decimal)  - 4294950912
Host address (hex)      - FFFFC000
Network address         - 255.255.192.0
Network mask            - 255.255.255.255
Network mask (bits)     - 32
Network mask (hex)      - FFFFFFFF
Broadcast address       - 255.255.192.0
Cisco wildcard          - 0.0.0.0
Addresses in network    - 1
Network range           - 255.255.192.0 - 255.255.192.0

Display results as HTML

$ ipcalc -h 192.168.0.1/255.255.128.0

For more options, please refer to man page:
$ man ipcalc
$ man sipcalc