CIDR / Subnet Calculator
Instantly get the network address, broadcast address, subnet mask, usable host range and total host count from any IPv4 CIDR notation — free, fully client-side, and built for network engineers, SOC analysts and students studying for networking certifications.
CIDR / Subnet Calculator
Enter an address in CIDR notation to get network range, broadcast address and host counts.
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes an IP address together with a slash and a prefix length — for example 192.168.1.0/24 — to describe how many bits of the address are dedicated to the network portion versus the host portion. It replaced older class-based addressing (Class A/B/C) and is the standard way subnets are defined in modern routing, firewall rules, and cloud VPC configuration.
Why analysts and engineers use a subnet calculator
During incident response, network segmentation reviews, firewall rule audits, or VLSM subnetting for a lab, manually converting a CIDR prefix into a subnet mask, broadcast address, and usable host range is slow and error-prone. This calculator does the binary math instantly and entirely in your browser — nothing you enter is sent to a server.
Frequently asked questions
What is CIDR notation?
CIDR notation combines an IP address with a slash and a prefix length, such as 192.168.1.0/24, to define a network's address range and subnet mask without relying on traditional class-based addressing.
How do I calculate a subnet mask from a CIDR prefix?
The CIDR prefix number (e.g. /24) indicates how many leading bits of the 32-bit IPv4 address are the network portion. A /24 prefix corresponds to a subnet mask of 255.255.255.0, leaving 8 bits for host addresses.
How many usable hosts does a subnet have?
Usable hosts equal 2 raised to the number of host bits, minus 2 — one address is reserved for the network identifier and one for the broadcast address. A /24 subnet, for example, has 254 usable host addresses.