What is an IP range calculator for CIDR?
An IP range calculator CIDR tool takes an IP address and subnet prefix (like /24) and instantly tells you the full subnet details:
network address, broadcast address, first and last usable host, subnet mask, wildcard mask, and host counts.
If you work with routers, firewalls, VPNs, cloud instances, VLANs, or ACL rules, this is one of the fastest ways to avoid addressing mistakes. Instead of manually doing binary math each time, you can verify ranges in seconds.
How to use this CIDR calculator
Step 1: Enter IPv4 CIDR notation
Type an address in the format IP/Prefix, such as 192.168.1.25/24.
The host portion can be any IP in that subnet; the tool will normalize it to the correct network.
Step 2: Click “Calculate Range”
The calculator computes all key values and displays them in a compact table. You can press Enter in the input field as a shortcut.
Step 3: Use the output in your network config
- Network Address: Base address of the subnet.
- Broadcast Address: Last address in subnet (except special cases).
- Usable Host Range: Assignable host addresses for devices.
- Subnet Mask: Dotted-decimal form of the prefix (e.g., /24 = 255.255.255.0).
CIDR quick reference (common blocks)
- /8 → 16,777,216 total addresses
- /16 → 65,536 total addresses
- /24 → 256 total addresses
- /27 → 32 total addresses
- /30 → 4 total addresses (common for point-to-point links)
- /31 → 2 addresses (RFC 3021 point-to-point usage)
- /32 → single host route
Understanding special subnet sizes
/31 networks
Historically, /31 had no usable host addresses in classic host/broadcast thinking. In modern practice (RFC 3021), /31 is valid for point-to-point links and both addresses are usable endpoints.
/32 networks
A /32 represents one specific IP address only. It is often used for loopback interfaces, policy routes, and precise firewall matching.
Common mistakes this tool helps prevent
- Using the wrong subnet mask when creating VLAN interfaces
- Overlapping DHCP scopes and static address blocks
- Incorrect firewall object ranges in ACLs
- Misconfigured cloud security rules due to prefix confusion
- Assigning a broadcast address to a host by accident
Final note
This calculator is designed for IPv4 CIDR calculations. For most day-to-day networking tasks, that covers the majority of troubleshooting and planning work. Keep it handy when designing subnets, validating infrastructure changes, or documenting network allocations.