IPv4 Subnet Calculator

What is IPv4 Subnet Calculator?

Planning VPC ranges, writing firewall rules, or carving up an office network all start with knowing exactly which addresses a CIDR covers. Enter 192.168.1.10/24 or an IP with a dotted mask (10.0.0.1/255.255.0.0) to get the network address, broadcast address, usable host range and count, netmask and wildcard, binary forms, plus the address class and public/private scope. Point-to-point /31 links (RFC 3021) and /32 host routes are handled per spec. You can also split the block into smaller subnets of any longer prefix. All computation is local.

How to Use

1. Enter a CIDR (e.g. 192.168.1.10/24) or IP + mask
2. Review the network address, usable host range and full details
3. Optionally enter a longer prefix below to split the block into smaller subnets

FAQ

Why does the usable host count subtract 2?

The first address of a block is the network address and the last is the broadcast address — neither can be assigned to a host, so a /24 with 256 addresses has 254 usable. Exceptions: both addresses of a /31 point-to-point link are usable (RFC 3021), and a /32 is a host route.

What is a wildcard mask for?

It is the bitwise inverse of the netmask, used in Cisco/Huawei ACLs and OSPF network statements: 0 means the bit must match, 1 means any value.

Does it support IPv6?

IPv4 and IPv6 are separate systems — use the IPv6 Subnet Calculator next door for IPv6.

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