Subnet Calculator & CIDR
Calculate IPv4 subnets, CIDR masks, network & broadcast IPs, and usable host ranges
About Subnet Calculator & CIDR
How Subnet Calculator & CIDR Works
Performs 32-bit unsigned bitwise arithmetic on IPv4 addresses and CIDR prefixes entirely in your browser. Computes bit boundaries, network IDs, broadcast addresses, and usable ranges with zero server queries.
Subnet Calculator & CIDR is a zero-server network planning utility for DevOps, cloud engineers, system administrators, and students. Enter an IPv4 address and CIDR prefix (or netmask) to instantly calculate the network address, broadcast address, netmask, wildcard mask, first and last usable host IPs, usable host capacity, IP classification, and private/public scope. It features an interactive binary bit visualizer showing the exact network and host bit boundary, plus an automatic subnet division planner to carve VPCs and clusters into child subnets.
Frequently asked questions
How are usable hosts calculated in a subnet?+
In standard subnets (/0 to /30), the total addresses is 2^(32 - prefix). Two addresses are reserved: the network address (all host bits 0) and the broadcast address (all host bits 1). Thus, usable hosts = 2^(32 - prefix) - 2. For /31 point-to-point links (RFC 3021), both addresses are usable (2 hosts). For /32 host routes, there is 1 host.
What are private RFC 1918 address ranges?+
Private ranges are reserved for local networks and cannot be routed on the public internet: 10.0.0.0/8 (10.0.0.0 – 10.255.255.255), 172.16.0.0/12 (172.16.0.0 – 172.31.255.255), and 192.168.0.0/16 (192.168.0.0 – 192.168.255.255).
Can I plan child subnets for AWS VPCs or Kubernetes clusters?+
Yes. Use the 'Subdivide Network' dropdown to split your parent CIDR block (such as a /16 or /24) into smaller /26, /27, or /28 subnets with automatic usable IP range and broadcast calculations.
Is any network configuration data sent to external servers?+
No. All calculations are executed 100% on-device using client-side JavaScript bitwise operators. Your internal network topologies and IP schemes remain completely private.
Limitations
This tool currently calculates IPv4 subnets (32-bit). IPv6 128-bit subnetting is planned for a future update.