IP version
IPv4 Subnet Calculation: CIDR, Masks and Host Ranges
For IPv4, a CIDR prefix specifies how many of the 32 bits identify a network. The calculator determines the network address, subnet mask, wildcard mask, broadcast address where applicable, number of addresses, and conventional usable-host range.
- Network address = IPv4 address bitwise AND subnet mask.
- Total addresses = 2(32 − prefix).
- Conventional usable hosts = total addresses − 2 for ordinary prefixes through /30.
- /31 has two point-to-point addresses under RFC 3021; /32 identifies a single host address.
Example: 51.235.55.121/30
For 51.235.55.121/30, the network is 51.235.55.120, mask 255.255.255.252, broadcast 51.235.55.123, and host range 51.235.55.121–51.235.55.122. There are four total IPv4 addresses, typically two usable on a conventional /30 subnet.
Quick IPv4 subnet mask reference
/24: 255.255.255.0 (256 addresses; typically 254 usable). /26: 255.255.255.192 (64; typically 62 usable). /27: 255.255.255.224 (32; typically 30 usable). /30: 255.255.255.252 (4; typically 2 usable).
IPv6 subnet and prefix calculations
IPv6 addresses contain 128 bits, and an IPv6 prefix is written such as 2001:db8::/64. IPv6 does not have IPv4-style broadcast addresses; interpretation differs from conventional IPv4 host counts. Select IPv6 in the existing form for its separate network calculations.
Frequently asked questions
What is CIDR notation?
CIDR writes an IP address followed by a slash and prefix length, such as 192.168.1.130/26. The prefix identifies the network portion.
How many usable IPv4 hosts are in a /24?
A conventional /24 network has 256 total addresses and typically 254 usable host addresses.
What is the subnet mask of /26?
A /26 mask is 255.255.255.192 and contains 64 IPv4 addresses, conventionally 62 usable.
What network contains 192.168.1.130/26?
The network is 192.168.1.128/26, with broadcast 192.168.1.191 and typical host range 192.168.1.129–192.168.1.190.
Can a /31 have two usable addresses?
Yes, for supported IPv4 point-to-point links under RFC 3021. It is not a conventional broadcast-capable LAN subnet.
What does /32 mean?
An IPv4 /32 designates one address, typically used as a host route.
Does this calculator support IPv6?
Yes. Select IPv6 and supply a valid IPv6 address and prefix. IPv6 has a 128-bit address space and no conventional broadcast address.
Why do results open in a new URL?
The result page stores the input address and prefix in its URL parameters so the calculation can be refreshed or shared. Avoid sharing confidential internal IP addresses.
Does the calculator test network connectivity?
No. It performs local address arithmetic and does not ping hosts, verify router settings, or change network configuration.
Related tools
Subnetting References and Practical Limits
A calculated range is not proof that an address is internet-reachable or configured on a specific network. Cloud providers can reserve extra IPs, and routers, VLANs, firewalls and routing tables affect the network actually in service. Network design should follow your organization’s address plan.
For the special /31 point-to-point rule, consult RFC 3021. The calculator does not collect traffic or scan addresses.
Find the result page by using the calculator above; unlike the main calculator URL, personalized result URLs are intentionally excluded from the sitemap and Google indexing.