Network Subnet Calculator

A network subnet calculator takes an IP address in CIDR notation — such as 192.168.1.0/24 — and computes the complete subnet breakdown: subnet mask, network address, broadcast address, first usable host, last usable host, and total usable host count. The /24 is the prefix length, indicating how many of the 32 bits in the IP address identify the network portion. The remaining bits identify individual hosts on that subnet.

This calculator runs entirely in your browser. No IP addresses or network configuration data are sent to any server — useful when working with internal or private IP ranges that should not leave your environment.

1. Enter an IP address in CIDR notation — type an IP address followed by a slash and prefix length, such as 192.168.1.0/24, into the input field.
2. Review the subnet breakdown — the calculator instantly displays the subnet mask, network address, broadcast address, first host, last host, and total usable host count.
3. Adjust the prefix length — change the /24 to another prefix (e.g. /28 or /16) to see how the subnet size and host count change in real time.
4. Copy or record the values — note the network address and broadcast address for use in firewall rules, routing tables, or cloud VPC configurations.

Classless Inter-Domain Routing (CIDR) notation is a compact way to represent an IP address and its subnet mask. Instead of writing 192.168.1.0 with a separate mask of 255.255.255.0, CIDR expresses both as 192.168.1.0/24. The prefix length after the slash tells you exactly how many bits are the network portion: /24 means 24 bits for the network, leaving 8 bits (256 addresses, 254 usable) for hosts. A /28 leaves only 4 bits for hosts (16 addresses, 14 usable).

• Network engineers configuring infrastructure who need to quickly verify subnet boundaries, host ranges, and broadcast addresses before applying firewall or routing rules.
• Developers working with cloud networking on AWS, GCP, or Azure who need to plan and validate CIDR blocks for VPCs, subnets, and security groups.
• Anyone studying for a networking certification (CCNA, CompTIA Network+) who needs to practice subnet calculations without doing binary arithmetic by hand.

• Privacy — all calculations run in your browser; no IP addresses or network data are sent to a server.
• Free — no account, no subscription, no rate limits.
• No account required — enter a CIDR block and see results immediately.
• Complete subnet breakdown — network address, broadcast address, subnet mask, first host, last host, and usable host count all in one view.

• Confusing /24 with Class C: Classful networking (Class A/B/C) was replaced by CIDR in 1993. A /24 is simply a prefix length — it happens to equal the old Class C range, but thinking in classful terms causes errors when working with non-standard prefix sizes like /22 or /27.
• Not accounting for network and broadcast addresses: Every subnet reserves two addresses — the network address (first) and broadcast address (last). A /24 has 256 total addresses but only 254 usable hosts. A /30 has 4 total but only 2 usable.
• Overlapping subnets in VPC design: When creating multiple subnets in a VPC, ensure CIDR blocks do not overlap. Overlapping ranges cause routing conflicts and broken connectivity that are difficult to diagnose after deployment.
• Using RFC 1918 ranges publicly: The ranges 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are private address spaces defined in RFC 1918 — they are not routable on the public internet. Never assign these to public-facing services.

For generating unique identifiers for network resources and VPC configurations, the UUID generator creates collision-free IDs. If you need to encode network configuration data for transmission, the Base64 encoder handles binary data safely.

Further reading: RFC 1918 — Private Address Space (IETF)

Planning a VPC CIDR block before deploying a cloud infrastructure stack — verify that the range is large enough for current and projected host counts. Verifying that two subnet ranges do not overlap when designing a multi-tier network with separate subnets for web, application, and database layers. Calculating the correct subnet mask to enter into a router, firewall, or network interface configuration. Practicing subnet math for a networking exam without needing to convert between binary and decimal by hand.