CIDR / Subnet Calculator
Enter an IP or CIDR notation to get mask, network / broadcast addresses and usable host range — all computed locally.
Computed entirely locally: the address never leaves your browser. A bare IP is treated as /32.
What CIDR notation means
192.168.1.0/24 means the first 24 bits are the network part, leaving 8 host bits — 256 addresses, 254 usable once network and broadcast are excluded. The calculator expands any CIDR into mask, range, wildcard and counts instantly.
Planning subnets
Splitting a /24 into four equal parts gives four /26s of 62 usable hosts each. Keep room for gateway and broadcast, and remember cloud providers reserve additional addresses inside VPC subnets.
Runs entirely locally
The calculation happens in your browser via BigInt arithmetic — nothing is sent to any server, and IPv6 ranges of any size are handled without precision loss.
Need the in-depth Chinese version? Read the full guide.
Related articles
Subnetting and CIDR Notation: A Practical Working Guide
From /24 to /30 — how to read, calculate, and carve up CIDR notation, with a manual verification method so subnetting stops being rote memorization at work.
Autonomous Systems (ASN): The Internet's Map of Carriers
What do AS4134 and AS13335 in IP lookup results mean? Autonomous systems (ASNs) are the internet's administrative map — read them and you can tell who an IP belongs to, how good it is, and whether it's a proxy.
What Is an IP Address? IPv4, IPv6, Public and Private, Explained in One Pass
A plain-language explanation of what IP addresses do, how IPv4 and IPv6 differ, how to tell public from private IPs, and why the IP you see isn't the one others see.
How IP Geolocation Works: Inside GeoIP Databases
Where GeoIP data comes from, how accurate it is, why it updates weekly, and why your result is sometimes off by a whole province.
More in the blog index
Frequently asked questions
Why does /24 show 254 usable hosts, not 256?
The first address is the network identifier and the last is broadcast. Neither can be assigned to a host, so a /24 yields 254 usable addresses.
Does it support IPv6?
Yes, with exact BigInt arithmetic — no floating-point shortcuts, so even a /12 IPv6 range computes correctly.
What is the wildcard mask used for?
Wildcard masks (the inverse of netmask) are used in ACL syntax on network gear — 0.0.0.255 matches the last octet range in access lists.