Find the usable IP address range for any CIDR block — the network address, broadcast address, and everything in between.
Enter an IP address and prefix length to see the network address, broadcast address, and everything usable in between.
Range: Network address + 1 to Broadcast address − 1
An IP range calculator answers a network planner's everyday question: given an address and a prefix, which addresses belong to the same block, and which of them can be handed out to devices? You enter an IPv4 address and a CIDR prefix, and the calculator returns the network address, the broadcast address and the usable host range in between, along with the number of usable hosts.
Network engineers use it when configuring DHCP scopes, writing firewall rules and access lists, or checking whether two devices are on the same subnet. It is also useful for students preparing for networking certifications and for anyone setting up office Wi-Fi, CCTV or a home lab who needs to know which addresses are free to assign without clashing with the router or the broadcast address.
1. Write the IP address and the prefix length, for example 192.168.10.77/27.
2. Find the block size: 2^(32 − prefix). For /27 this is 32 addresses.
3. Find the network address by rounding the IP down to a multiple of the block size in the octet where the mask ends. In binary, this is IP AND mask.
4. Broadcast address = Network address + Block size − 1.
5. Usable range = Network + 1 to Broadcast − 1, giving 2^(32 − prefix) − 2 hosts.
6. For /31 and /32 the minus-two rule does not apply: a /31 has 2 usable addresses on a point-to-point link and a /32 is a single host.
A prefix of /n fixes the first n bits of every address in the block. The remaining 32 − n bits can take any value, from all 0s to all 1s. All 0s gives the lowest address, the network address. All 1s gives the highest, the broadcast address. Because the host bits start from zero, every block begins at a multiple of its size. That is why a /27 block can start at .64 or .96 but never at .77, and why 192.168.10.77 falls in the block that starts at .64.
In a normal subnet, the network address identifies the subnet itself in routing tables, and the broadcast address reaches every host on the subnet at once. Assigning either to a device would cause confusion, so the usable count is block size minus 2. RFC 3021 later allowed /31 subnets on point-to-point links, where there are only two devices and no need for a broadcast, so both addresses are usable. A /32 names a single host, common for loopbacks and host routes.
The usable range is the maximum pool, not the recommended DHCP pool. In practice, the first or last usable address goes to the gateway, and a few more are kept for printers, switches, access points and servers with fixed addresses. The DHCP scope is then set to the rest. Planning with the full block size in mind, and leaving space for growth, avoids renumbering later when the number of devices outgrows a small subnet.
Imtiaz is setting up a separate CCTV network at a Chennai showroom. The camera vendor has given him 192.168.10.77/27, and he needs to know which addresses he can assign to cameras and the NVR.
Answer: Usable IP range 192.168.10.65 – 192.168.10.94; Network address 192.168.10.64; Broadcast address 192.168.10.95
Assuming the block starts at the IP you were given instead of the nearest lower boundary.
Assigning the network or broadcast address to a device.
Setting a DHCP scope over the gateway or statically assigned addresses.
Forgetting that /31 and /32 do not follow the minus-two rule.
Planning DHCP scopes for office, CCTV or IoT networks.
Writing firewall rules or access lists for a specific range.
Checking whether two devices are in the same subnet.
Practising subnetting for CCNA or similar exams.
How is this different from the Subnet Calculator?
It's the same underlying calculation, focused specifically on the usable IP range rather than the full binary breakdown the Subnet Calculator provides.