CIDR / Subnet Calculator
Enter an IP with a prefix (192.168.1.0/24, 2001:db8::/32) or with a netmask and get the network, broadcast, host range, counts and masks. Split a block into smaller subnets or test whether an address belongs to it.
Runs in your browser — nothing is uploaded.
IPv4 or IPv6. A single address is treated as /32 or /128.
Block details
Is an address in the range?
Must be the same IP version.
Split into subnets
Longer than the current prefix, for example 26.
How to use it
- Type an address with a prefix (10.0.0.0/16), an address and a netmask (10.0.0.1 255.255.0.0), or an IPv6 block.
- Read the network, broadcast, usable range, counts and masks, and copy what you need.
- To divide the block, choose a longer prefix. To test an address, enter it in the range check.
Frequently asked questions
What does /24 mean?
The first 24 bits of the address identify the network and the remaining 8 bits identify hosts. In IPv4, /24 is the netmask 255.255.255.0 and gives 256 addresses.
Why are 2 addresses missing from the host count?
In IPv4 the first address of a block is the network address and the last is the broadcast address, so a /24 has 254 usable hosts. The exceptions are /31 (point-to-point links, RFC 3021, both addresses usable) and /32 (a single host).
What is the wildcard mask?
The inverse of the netmask (0.0.0.255 for /24). Cisco ACLs and OSPF configurations use it.
How does IPv6 differ?
IPv6 has no broadcast address and no network/host reservation in this tool, so the first and last addresses of the block are both reported as usable. Counts are exact, even for the 2^64 addresses of a /64.
Is the IP I enter sent anywhere?
No. Everything is calculated in your browser, nothing is looked up.