IPv4 CIDR & Subnet Calculator
A tool that calculates the network address, subnet mask, last address, total addresses, and usable hosts from IPv4 CIDR notation such as 192.168.10.0/24. It also checks whether given IP addresses fall within the range, which is handy for allowlists and network settings — all processed in your browser.
Result
Enter a CIDR block such as 192.168.10.0/24 to see the network range.
How to use
- Enter an IPv4 address and prefix length in CIDR notation, such as 192.168.10.0/24.
- The network address, subnet mask, range, total addresses, and usable hosts are shown.
- Enter IPv4 addresses to check, one per line, to see whether each one is in range.
About this tool
Firewalls, cloud security groups, and allowlists specify IP ranges in CIDR notation. This tool shows which addresses a range covers and whether the server IPs you want to allow are inside it.
If the address includes host bits, as in 192.168.10.37/24, it's normalized to the network 192.168.10.0/24 and a note is shown. Total addresses counts every address in the range, while usable hosts excludes the network and broadcast addresses. /31 (point-to-point) and /32 (a single address) are handled separately.
IPv6 and real network connections are not covered. Numbers with leading zeros (such as 010) are rejected because some systems read them as octal.
Enter 192.168.1.130/26. The network is 192.168.1.128/26, the mask is 255.255.255.192, and the range ends at 192.168.1.191. Checking 192.168.1.190 reports in range; 192.168.1.192 is out of range.
Being in range differs from being assignable to a host. In this example, 192.168.1.191 is included but serves as the broadcast address, so usable hosts end at .190. Use the full range for allowlist membership and the usable-host range when planning device assignments.
Frequently asked questions
Why does /24 have 254 usable hosts?
Of the 256 addresses, the first (network) and last (broadcast) can't be assigned to hosts.
How are /31 and /32 handled?
/31 shows both addresses as usable for point-to-point links per RFC 3021, and /32 shows its single address as usable.
Is IPv6 supported?
This version supports IPv4 only.