Calculate IPv4 & IPv6 subnets — network, broadcast, mask, and host range
Free subnet calculator and CIDR calculator for network engineers and developers. Enter an IP and prefix to get network address, broadcast, subnet mask, wildcard mask, usable hosts, and host range. Supports IPv4 subnet calculator and IPv6 prefix modes. 100% client-side — your IPs never leave the browser.
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| Subnet (CIDR) | Network | Broadcast |
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Click any row to apply that CIDR prefix in the IPv4 calculator. Subnet mask, wildcard mask, and host counts for /0 through /32.
| CIDR | Subnet Mask | Wildcard | Usable Hosts | Total Addresses |
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Click any row to load that prefix in the calculator
CIDR (Classless Inter-Domain Routing) replaces old classful networks (Class A, B, C) with flexible prefix lengths. An address like 10.0.5.20/22 means the first 22 bits identify the network; the remaining 10 bits are for hosts.
To find the network address, bitwise-AND the IP with the subnet mask. To find the broadcast, OR the network with the inverted mask (wildcard mask).
The subnet mask uses 1s for network bits and 0s for host bits. A wildcard mask flips this — 0s where bits must match, 1s where bits are ignored. ACLs on Cisco gear use wildcard masks: 0.0.0.255 matches any host in the last octet.
IPv6 subnets are almost always /64 on LANs — one subnet per interface with a vast address space. fc00::/7 is Unique Local (ULA, like private IPv4). fe80::/10 is link-local. Use the IPv6 tab above for prefix calculations.
A subnet calculator computes network details from an IP address and CIDR prefix or subnet mask: network address, broadcast, host range, mask, wildcard, and usable host count.
CIDR notation appends a slash and prefix length to an IP, e.g. 192.168.1.0/24. The number 24 means 24 network bits — mask 255.255.255.0 and 254 usable hosts.
A /24 has 256 total addresses. Subtract network and broadcast for 254 usable hosts. Mask: 255.255.255.0.
Subnet mask marks network bits (1s). Wildcard mask is the inverse — used in ACLs. For /24: mask 255.255.255.0, wildcard 0.0.0.255.
/30 gives 4 addresses (2 usable) — ideal for router-to-router point-to-point links with minimal waste.
RFC 1918: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Not routable on the public internet.
Add consecutive 1 bits left to right in a 32-bit word. /24 → 255.255.255.0. This tool converts automatically when you change the prefix slider.
VLSM uses different prefix lengths in one network. Split a /24 into four /26 subnets using the Split Subnet section above.
IPv6 uses 128-bit addresses. Typical LAN prefix is /64. Enter an address in the IPv6 tab to see expanded, compressed, and network prefix forms.
Network address = all host bits 0. Broadcast = all host bits 1. Neither is assigned to a host interface.
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/32 is a single-host route with mask 255.255.255.255 — one IP, often used for host routes or loopbacks.