CIDR Calculator
Enter an IP address and CIDR prefix to get the network range, subnet mask, and usable host count.
Inputs
Any address in the block, e.g. 192.168.1.0
0–32
CIDR Block
192.168.1.0/24
Network Address
192.168.1.0
Broadcast Address
192.168.1.255
Usable Host Range
192.168.1.1 – 192.168.1.254
Subnet Mask
255.255.255.0
Total Addresses
256
Usable Hosts
254
Step by step
Values used
IPv4 Address = 192.168.1.0; CIDR Prefix = 24 /
Usable hosts from prefix
hosts = 2^(32 − prefix) − 2
CIDR Block
= 192.168.1.0/24
Network Address
= 192.168.1.0
Broadcast Address
= 192.168.1.255
Usable Host Range
= 192.168.1.1 – 192.168.1.254
Subnet Mask
= 255.255.255.0
Total Addresses
= 256
How it works
CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length that states how many leading bits form the network portion. The remaining bits identify hosts within that network. The network address is found by ANDing the IP with the mask derived from the prefix, and the broadcast address is the network ORed with the inverse mask. Usable hosts are the total addresses in the block minus the network and broadcast addresses (2^(32−prefix) − 2), except for the /31 point-to-point (RFC 3021) and /32 host-route special cases.
Formula
Usable hosts from prefix
hosts = 2^(32 − prefix) − 2
- p
- CIDR prefix length (0–32)
Guides that use this calculator
Frequently Asked Questions
What is CIDR notation?
CIDR notation writes an IP address followed by a slash and a number (e.g. 192.168.1.0/24), where the number is the count of leading bits that make up the network portion of the address.
How is the number of usable hosts calculated?
Usable hosts = 2^(32 − prefix) − 2. The subtraction removes the network address and the broadcast address, which cannot be assigned to hosts. /31 subnets (point-to-point links) and /32 (single host) are exceptions per RFC 3021.
Why does a smaller prefix mean a bigger network?
The prefix counts network bits; fewer network bits leaves more host bits, which doubles the address space for every bit removed. A /23 has twice the addresses of a /24.
Does the entered IP need to be the network address?
No — any address inside the block works. The calculator ANDs your address with the derived mask to find the actual network address for you.