Subnet / CIDR Calculator
Subnet calculation from CIDR notation — network & broadcast address, usable IP range, subnet/wildcard mask, IP class and reverse DNS. Supports IPv4 and IPv6.
What is CIDR?
CIDR (Classless Inter-Domain Routing) is the notation for writing an IP network together with its size, e.g. 192.168.1.0/24. The number after the slash — the prefix length — tells you how many bits belong to the network portion and how many are left for hosts.
What does this tool calculate?
- Network address — the base of the subnet (its first IP).
- Broadcast address — the last IP of the subnet (IPv4 only).
- Usable hosts — the address range you can assign to devices (network & broadcast excluded).
- Subnet & wildcard mask — the mask in dotted-decimal and its inverse (handy for ACLs).
- IP class, type (public/private), binary, hex and the reverse DNS (PTR) zone.
How do I read the prefix?
The larger the prefix, the smaller the network:
/24 → 256 addresses (254 usable) — typical LAN /25 → 128 addresses (126 usable) /26 → 64 addresses ( 62 usable) /30 → 4 addresses ( 2 usable) — point-to-point link /32 → 1 address — single host
The calculation runs 100% in your browser in real time — nothing is sent to the server as you type. Both IPv4 and IPv6 are supported, as well as mask input (e.g.
192.168.1.0 255.255.255.0).Frequently Asked Questions
Why does a /24 have 256 but only 254 usable?
Two addresses are always reserved: the network address (first) and the broadcast address (last). So a /24 leaves 254 for devices.
What do /31 and /32 mean?
/32 is a single host address. /31 (RFC 3021) is used on point-to-point links and provides 2 usable addresses with no broadcast.What is a wildcard mask?
It is the inverted subnet mask (bit-flip). For example
255.255.255.0 becomes 0.0.0.255. It is used in access control lists (ACLs) on Cisco and other routers.Which are the private address ranges?
Per RFC 1918:
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. They are not routed on the public internet and are used in internal networks.Is IPv6 supported?
Yes. Enter e.g.
2001:db8::/48 to see the network/last address, total address count and type. IPv6 has no broadcast and no reserved first/last address.