CIDR / Subnet Calculator
Compute network, broadcast, netmask and host range from an IPv4 CIDR block.
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About CIDR / Subnet Calculator
This CIDR calculator (also called a subnet calculator) takes an IPv4 address with a prefix length, such as 192.168.1.10/24, and works out everything about the block it belongs to: the network address, broadcast address, subnet mask, wildcard mask, first and last usable host, and how many addresses the block contains.
It is useful when you are planning a home or office network, writing firewall rules or cloud security groups, or just double-checking that two ranges do not overlap. Results update as you type and each value has its own copy button. The maths is done in your browser.
How to use
- Type an address and prefix into the IPv4 CIDR field, for example 10.0.0.0/16 or 192.168.1.10/24.
- Read the results: Network, Broadcast, Netmask, Wildcard, First host, Last host, Total addresses and Usable hosts.
- Click the copy button next to any row to copy just that value.
- Change the prefix number to compare how big different subnets are.
FAQ
What does the /24 in CIDR notation mean?+
It is the prefix length: how many of the 32 bits in an IPv4 address identify the network. A /24 leaves 8 bits for hosts, giving 256 addresses and a subnet mask of 255.255.255.0. Each step down (/23, /22 and so on) doubles the size of the block.
Why are usable hosts two fewer than total addresses?+
In a normal subnet the first address is the network address and the last is the broadcast address, so neither is assigned to a device. The calculator subtracts those two. The exceptions are /31, where both addresses are usable for point-to-point links (RFC 3021), and /32, which is a single host.
Can I enter any IP inside the subnet, not just the network address?+
Yes. Enter any address with a prefix and the calculator masks it to find the network it belongs to. For example 192.168.1.77/26 gives the network 192.168.1.64.
What is a wildcard mask?+
It is the subnet mask with every bit flipped, so 255.255.255.0 becomes 0.0.0.255. Cisco access lists and some OSPF settings use wildcard masks instead of subnet masks.
Does it support IPv6?+
No, this subnet calculator handles IPv4 only. It also requires the prefix, so an address without a slash and a number from 0 to 32 shows an error.