Subnet Calculator
Calculate network address, broadcast, and usable IP ranges from CIDR notation.
What Is a Subnet Calculator?
A subnet calculator computes network addressing details from CIDR (Classless Inter-Domain Routing) notation. Subnetting divides a large IP address space into smaller, more manageable sub-networks.
Common CIDR Ranges
Common Use Cases
- Network planning — determine how many usable IP addresses a subnet provides before allocating it to a department or VLAN.
- Cloud VPC design — plan non-overlapping subnet ranges when setting up cloud infrastructure across multiple availability zones.
- Troubleshooting connectivity — verify whether two devices are actually on the same subnet when diagnosing local network communication issues.
- Documentation — quickly generate network/broadcast addresses and host ranges for network diagrams.
Example
A /24 subnet (255.255.255.0) provides 254 usable host addresses — suitable for a single office or rack — while a /16 provides over 65,000, more appropriate for a large enterprise or cloud VPC.
Frequently Asked Questions
What's the difference between network and broadcast address?
The network address identifies the subnet itself and can't be assigned to a device. The broadcast address is used to send data to every device on that subnet simultaneously — also not assignable.
How many usable hosts does a /30 provide?
A /30 provides 4 total addresses, 2 of which are usable for hosts (network and broadcast take the other 2) — commonly used for point-to-point links.
What is CIDR notation?
CIDR (e.g. /24) is a shorthand for expressing how many bits of an IP address are used for the network portion, which determines subnet size.
Why do cloud providers reserve extra IPs per subnet?
Providers like AWS reserve a handful of addresses per subnet (beyond network/broadcast) for internal routing and DNS purposes, slightly reducing usable host count.