What is an IP Subnet Calculator?
Every VPC, firewall rule and router config speaks CIDR, and off-by-one subnet math causes real outages.
Enter any IPv4 CIDR for the network and broadcast addresses, dotted netmask, first/last usable host, and exact counts: including correct /31 and /32 handling.
Frequently asked questions
Why usable hosts = total − 2?
The lowest address names the network and the highest is broadcast. /31 point-to-point links (RFC 3021) and /32 single hosts are the exceptions.
What does /24 actually mean?
The first 24 bits are the network: leaving 8 bits = 256 addresses, 254 usable.
How do I split a network into subnets?
Increase the prefix: a /24 splits into two /25s or four /26s. Calculate each child here.
IPv6 support?
IPv4 only for now. IPv6 prefix math is planned.