Subnet & CIDR Calculator

Enter an IPv4 address with a prefix length (/24) or subnet mask to get the network and broadcast addresses, usable IP range and host count, with binary working and a subnet split table.

How to use

  1. Type an IP with a prefix, such as 192.168.0.10/24, or with a mask, such as 192.168.0.10 255.255.255.0.
  2. The network address, broadcast address, mask, wildcard, usable range and host count appear immediately.
  3. To split the block, enter the new prefix length (for example 26 turns a /24 into four /26 subnets).
  4. Turn on the step-by-step explanation to see the bitwise working, and use the copy buttons to take the results.

FAQ

How is the number of usable hosts calculated?

The block has 2^(32 - prefix) addresses. For /30 and shorter prefixes the first (network) and last (broadcast) addresses are not hosts, so usable hosts = 2^(32 - prefix) - 2. A /24 has 256 - 2 = 254.

Why are /31 and /32 handled differently?

Under RFC 3021 a /31 is a point-to-point link and both addresses are usable hosts (2 hosts). A /32 is a single-host route (1 host).

Why is the mask 255.0.255.0 rejected?

A valid subnet mask is a run of 1 bits followed by 0 bits. Non-contiguous masks, and wildcard values such as 0.0.0.255, are not accepted as masks.

What if the IP I enter is not the network address?

The address is ANDed with the mask and the result is calculated for the network it belongs to, with a notice. For example 172.16.5.9/12 becomes 172.16.0.0/12, which spans 172.16.0.0 to 172.31.255.255.

Which ranges are shown as private?

Only blocks that fit entirely inside the RFC 1918 ranges 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Special ranges such as loopback or CGNAT (100.64.0.0/10) are not singled out. IPv6 is not supported.

AI agents: this calculation is available over an API without the form — see /llms.txt and the tool list at /api/calc; confirm the final result on this page.

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