IP Subnet Calculator
Calculate network address, broadcast, usable host range, subnet mask and host count from any IPv4 address and CIDR prefix. Free and instant.
About the IP Subnet Calculator
This IP subnet calculator turns an IPv4 address and CIDR prefix into every number you need to plan or troubleshoot a network. Enter something like 192.168.1.10/24 and it instantly shows the network address, broadcast address, usable host range, total and usable host counts, subnet mask, wildcard mask and the address class.
It handles the edge cases real networks hit: /31 point-to-point links (RFC 3021) and /32 single hosts report their addresses correctly instead of subtracting non-existent network and broadcast rows. The tool also tells you whether the address is public or falls in a private, loopback or link-local range, and shows the mask in binary so subnetting makes intuitive sense.
All calculation runs in your browser using plain bit arithmetic — nothing is sent anywhere — so it is fast, private and works offline. Copy the full breakdown to your clipboard for tickets or documentation with one click.
How to Use the IP Subnet Calculator
- 1Enter an IPv4 address, or paste CIDR notation like 10.0.0.0/8 directly.
- 2Set the CIDR prefix length between 0 and 32.
- 3Click Calculate subnet to see the network details and usable range.
- 4Copy the full breakdown for your documentation.
Frequently Asked Questions
What is a CIDR prefix?
CIDR (Classless Inter-Domain Routing) notation writes a subnet mask as a slash and a number, like /24, meaning the first 24 bits identify the network. /24 equals the mask 255.255.255.0 and leaves 8 bits (256 addresses) for hosts. Smaller numbers mean bigger networks.
Why are usable hosts two fewer than total addresses?
In a normal subnet the first address is reserved as the network identifier and the last as the broadcast address, so neither can be assigned to a device. A /24 has 256 total addresses but 254 usable ones. The exceptions are /31 and /32, which this calculator handles specially.
What's the difference between the subnet mask and the wildcard mask?
The subnet mask (e.g. 255.255.255.0) marks network bits with 1s. The wildcard mask is its inverse (0.0.0.255) and marks host bits with 1s — it's the form Cisco ACLs and OSPF configurations expect, which is why both are shown.
How do I know if an address is private?
The tool flags RFC 1918 private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), loopback (127.0.0.0/8) and link-local (169.254.0.0/16) as 'Private / reserved'. Everything else is labelled Public, meaning it is routable on the internet.
Does it work for IPv6?
This calculator is for IPv4. For IPv6 addresses, use the IPv6 Compressor and Expander to normalise notation — full IPv6 subnetting uses 128-bit arithmetic and much larger address spaces.