Subnet Calculator
About the Subnet Calculator
Calculate everything about an IPv4 or IPv6 network from CIDR notation: network and broadcast addresses, the usable host range, number of hosts, subnet mask, wildcard mask, address type and class. A colour-coded binary view shows exactly which bits belong to the network and which to hosts. Split any block into smaller equal subnets, convert addresses between dotted, integer, hex and IPv4-mapped IPv6 forms, and use the built-in CIDR cheat sheet. Everything is calculated instantly on your device.
This tool works in your browser: the files and text you use are processed on your device and are not uploaded.
How to use it
- Type an address with a prefix (192.168.1.10/24), with a mask (10.0.0.1 255.255.0.0), or an IPv6 block (2001:db8::/48).
- Change the prefix from the dropdown or the cheat sheet to see how the network changes.
- Use “Split into subnets” to divide the block and copy the list.
Frequently asked questions
Why are 2 addresses subtracted from usable hosts?
In IPv4 the first address of a subnet identifies the network and the last is the broadcast address, so neither can be given to a device. The exceptions are /31 point-to-point links (both addresses usable, RFC 3021) and /32 single hosts. IPv6 has no broadcast address.
What is a wildcard mask?
The inverse of the subnet mask — host bits are 1 and network bits are 0. For a /24 (255.255.255.0) it is 0.0.0.255. Cisco ACLs and OSPF configuration use wildcard masks.
What does /24 mean in CIDR notation?
It is the number of leading bits that make up the network part of the address. A /24 IPv4 network has 24 network bits and 8 host bits, which gives 256 addresses (254 usable hosts).
Which IP ranges are private?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are private IPv4 ranges (RFC 1918). 100.64.0.0/10 is used for carrier-grade NAT. In IPv6, fc00::/7 is the unique-local (private) range and fe80::/10 is link-local. The calculator labels these automatically.
What size subnet should an IPv6 LAN use?
Standard practice is a /64 for every LAN segment, because features like SLAAC address auto-configuration require it. Sites are commonly given a /48 or /56, which contains 65,536 or 256 /64 subnets.