IP Subnet Calculator
Calculate network addresses, host ranges, broadcast addresses, and subnet details from any IP address and CIDR prefix length.
Enter Subnet Details
CIDR Notation Quick Reference
| CIDR | Subnet Mask | Total Addresses | Usable Hosts | Typical Use |
|---|---|---|---|---|
| /24 | 255.255.255.0 | 256 | 254 | Standard office LAN |
| /25 | 255.255.255.128 | 128 | 126 | Medium department |
| /26 | 255.255.255.192 | 64 | 62 | Small department / VLAN |
| /27 | 255.255.255.224 | 32 | 30 | Server farm, Wi-Fi segment |
| /28 | 255.255.255.240 | 16 | 14 | Small server group |
| /29 | 255.255.255.248 | 8 | 6 | Point-to-point links |
| /30 | 255.255.255.252 | 4 | 2 | Router-to-router link |
Usable hosts exclude the network address and broadcast address. For point-to-point links, /31 (2 addresses) is sometimes used per RFC 3021. Talk to our network team
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Frequently asked questions
A subnet mask defines which part of an IP address identifies the network and which part identifies individual devices. It determines how many usable host addresses are available within a subnet, which matters directly for network planning - undersizing a subnet means running out of IP addresses as your office grows.
Usable hosts equal 2 to the power of the number of host bits, minus 2 (one address reserved for the network identifier, one for the broadcast address). A /24 subnet, for example, gives 254 usable addresses. This calculator works it out automatically from any CIDR notation or subnet mask you enter.
CIDR notation, such as /24, is shorthand for a subnet mask like 255.255.255.0 - the number after the slash represents how many bits are used for the network portion. Both describe the same thing; CIDR is just the more compact format commonly used in routing and firewall configuration.
Segment by function - separate subnets for staff devices, guest WiFi, VoIP phones, and servers improve both security and performance. Size each subnet with headroom for growth rather than the exact current device count, since renumbering a live network later is disruptive and best avoided.
