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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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