Calculate network addresses, subnet masks, broadcast addresses, host ranges and more — for IPv4 and IPv6.
Enter an IPv4 address with CIDR prefix (0–32) or dotted-decimal subnet mask
Quick reference for network engineers, students and sysadmins — covering IPv4 CIDR, common formulas, private ranges and IPv6 prefixes.
| CIDR | Subnet Mask | Wildcard | Hosts | Use Case |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,214 | Class A / large ISP |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,534 | Class B / campus |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,094 | Large office LAN |
| /21 | 255.255.248.0 | 0.0.7.255 | 2,046 | Medium campus |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,022 | Medium LAN |
| /23 | 255.255.254.0 | 0.0.1.255 | 510 | Medium office |
| /24 | 255.255.255.0 | 0.0.0.255 | 254 | ★ Standard LAN / Class C |
| /25 | 255.255.255.128 | 0.0.0.127 | 126 | Half a /24 |
| /26 | 255.255.255.192 | 0.0.0.63 | 62 | Quarter of /24 |
| /27 | 255.255.255.224 | 0.0.0.31 | 30 | Small office VLAN |
| /28 | 255.255.255.240 | 0.0.0.15 | 14 | Very small segment |
| /29 | 255.255.255.248 | 0.0.0.7 | 6 | Small link / DMZ |
| /30 | 255.255.255.252 | 0.0.0.3 | 2 | ★ Point-to-point link |
| /31 | 255.255.255.254 | 0.0.0.1 | 2* | P2P (RFC 3021) no BC |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | Host route / loopback |
| Prefix | Range / Example | Purpose | RFC |
|---|---|---|---|
| ::1/128 | ::1 | Loopback (localhost) | RFC 4291 |
| fe80::/10 | fe80::… | Link-local (auto-config) | RFC 4291 |
| fc00::/7 | fd00::… | Unique Local (ULA = private) | RFC 4193 |
| 2000::/3 | 2001:… | ★ Global Unicast (public) | RFC 4291 |
| ff00::/8 | ff02::1 | Multicast | RFC 4291 |
| 2001:db8::/32 | 2001:db8::1 | Documentation & examples only | RFC 3849 |
| 64:ff9b::/96 | 64:ff9b::x.x.x.x | IPv4-mapped IPv6 (NAT64) | RFC 6052 |
/64 subnet contains 2⁶⁴ ≈ 18.4 quintillion addresses — assign one per LAN segment without worrying about address exhaustion./30 for point-to-point links, /24 for workstations, /27 for servers — saving addresses versus fixed-length subnetting.This free IP subnet calculator supports both IPv4 and IPv6 protocols. Enter any IP address in CIDR notation (e.g. 192.168.1.0/24) and instantly get the complete subnet breakdown.
Subnetting divides a large IP network into smaller, manageable sub-networks (subnets). It improves network performance, security and address efficiency. A subnet mask determines which portion of an IP address identifies the network versus the individual host.
CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its associated prefix length as a single string — for example 192.168.0.0/24. The number after the slash (the prefix length) indicates how many bits represent the network portion. A /24 gives 256 addresses (254 usable hosts); a /30 gives 4 addresses (2 usable hosts), ideal for point-to-point links.
IPv4 uses 32-bit addresses in dotted-decimal notation (e.g. 192.168.1.1), providing approximately 4.3 billion addresses. IPv6 uses 128-bit addresses in hexadecimal notation (e.g. 2001:db8::1), providing a virtually unlimited address space. IPv6 prefixes range from /0 to /128.
RFC 1918 defines three private IPv4 address ranges reserved for internal network use: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. These addresses are not routable on the public internet.
A wildcard mask is the bitwise inverse of the subnet mask. It is used in Cisco ACLs (Access Control Lists) and OSPF configurations to specify which bits of an address must match. For example, a subnet mask of 255.255.255.0 has a wildcard mask of 0.0.0.255.
Last updated: January 2026
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Last updated: January 2026
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Last updated: January 2026
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