IP Subnet Calculator (CIDR)
Network address, broadcast address, host range and host count from an IP address and mask
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Calculates the network address, broadcast address, usable host range and host count from an IPv4 address and a subnet mask or CIDR prefix such as /24. Use it when you plan a network or work through a subnetting exercise.
How to use
- Type an address such as 192.168.1.10 in "IPv4 address" and choose the "Subnet mask (prefix)". You can also type 192.168.1.10/24 or 192.168.1.10 255.255.255.0 in one box.
- The "Usable host range", network and broadcast addresses, wildcard mask and "Address type" appear at once. "Binary view" colours the network bits and host bits.
- To divide the network, use the "Split equally" or "VLSM" tab; to combine several ranges, use "Summarize".
- Check whether an address belongs to a network on "Is it in the range?", and work with IPv6 short forms and ranges on the "IPv6" tab.
How it works
- A block has 2^(32 − prefix) addresses. Usable hosts are that number minus 2, the network and broadcast addresses; a /31 counts 2 (RFC 3021) and a /32 counts 1.
- "Address type" names private, loopback, carrier-grade NAT and other special blocks from the IANA special-purpose address registry (updated 2025-10-09).
- All calculations run on this device. The tool never looks up, pings or contacts any address.
Questions and answers
- How many hosts are in a /24 subnet?
- A /24 has 2^8 = 256 addresses, and 254 are usable after the network and broadcast addresses are removed. A /26 has 64 addresses, of which 62 are usable.
- What is 255.255.255.0 in CIDR notation?
- It is /24. The prefix is the number of 1 bits in the mask, so 255.255.255.192 is /26 and 255.255.0.0 is /16.
- What are the network address and the broadcast address?
- The network address is the first address of the block, with all host bits set to 0. The broadcast address is the last one, with all host bits set to 1. For 192.168.1.10/24 they are 192.168.1.0 and 192.168.1.255.
- What are the private IP address ranges?
- They are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. An address from these ranges is shown as "Private network" under "Address type".