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IP / CIDR Subnet Calculator

Enter an IPv4 address in CIDR notation (e.g. 192.168.1.10/24) to instantly calculate the network and broadcast addresses, usable host range, host count, subnet mask, and wildcard mask.

All processing runs locally in your browser — nothing is sent to any server.

Guide: How to use & features

  • Type an "IP/prefix" value such as 10.0.0.0/8. If you omit the prefix, it is treated as /32.
  • The network, broadcast, host range, and other values are computed automatically as you type.
  • Use the copy button next to each row to copy an individual value to your clipboard.
  • Special prefixes such as /31 (RFC 3021 point-to-point links) and /32 (single hosts) are handled correctly.

FAQ: FAQ

  • Why do "total addresses" and "usable hosts" differ?

    In a normal subnet the first address (network) and the last address (broadcast) cannot be assigned to hosts, so usable hosts equals total addresses minus two. For example, a /24 has 256 total addresses and 254 usable hosts.
  • Why does the host count behave differently for /31 and /32?

    A /32 represents a single host, so the one address is used as-is. A /31 is intended for point-to-point links per RFC 3021 and reserves neither a network nor a broadcast address, so both addresses are usable. This tool handles these special cases.
  • What is the wildcard mask?

    It is the bitwise inverse of the subnet mask, used mainly in Cisco-style ACLs (access control lists) to specify address ranges. For a mask of 255.255.255.0, the wildcard mask is 0.0.0.255.
  • Is the IP address I enter sent anywhere?

    No. All calculations run locally in your browser via JavaScript, and the values you enter are never sent to a server, so it is safe to use even when planning internal networks.

Use cases: Common Use Cases

  • Verifying subnet designs

    When splitting into /24, /26, and so on, quickly check that the usable host count and range of each subnet meet your requirements.

  • Defining firewall / ACL ranges

    Confirm the network address and wildcard mask to write allow/deny ranges in your rules accurately.

  • Planning cloud VPC / subnet CIDRs

    When choosing CIDRs for VPCs and subnets on AWS, GCP, and others, understand the host limits and address ranges in advance.

Notes: Notes & Limitations

  • IPv4 only

    This tool targets IPv4 CIDR. IPv6 addresses (e.g. 2001:db8::/32) are not supported.

  • How usable hosts are counted

    Normal subnets of /30 and larger exclude the network and broadcast addresses. /31 and /32 are treated as special cases where all addresses are counted as usable.

  • Scope of the private check

    The "address type" flags RFC 1918 private ranges, loopback, and link-local. Everything else is shown as public, but this does not guarantee actual reachability.

Results

Network CIDR
Subnet mask
Wildcard mask
Network address
Broadcast address
Usable host range
Total addresses
Usable hosts
Address type

Enter a CIDR above to see the breakdown.

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