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Compute netmask, network, broadcast, and host range from CIDR.
🔒 Accepted inputs: 192.168.1.10/24, 192.168.1.10/255.255.255.0, or 192.168.1.10 255.255.255.0. Edge cases follow the RFCs: /31 is a point-to-point link with 2 usable addresses (RFC 3021) and /32 identifies a single host.
Subnetting is the arithmetic every network engineer does daily: given an address like 192.168.1.10/24, which network does it belong to, what is its broadcast address, and how many hosts fit inside? This calculator answers instantly with the subnet mask, wildcard mask, network and broadcast addresses, usable host range, address class, and RFC 1918 private/public classification — all computed locally in your browser with exact 32-bit binary math.
An IPv4 address is a 32-bit number, and the prefix length (/24) says how many leading bits identify the network. The subnet mask is those bits set to 1; the wildcard mask is its inverse, used in Cisco ACLs and OSPF. AND-ing the address with the mask yields the network address; OR-ing with the wildcard yields the broadcast address. Everything between them — minus those two reserved addresses — is the usable host range: 2^(32−prefix) − 2 hosts.
Two prefixes break the "minus two" rule. /31 links (RFC 3021) are point-to-point WAN links with no network or broadcast address at all — both addresses are usable, which halves address waste on router-to-router links. /32 identifies exactly one host and is common for loopback interfaces and firewall rules. This tool handles both correctly instead of reporting zero usable hosts.
Classful labels survive mostly in documentation: class A (1–126), B (128–191), C (192–223), D (multicast), and E (experimental). What matters operationally is RFC 1918: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are private and unroutable on the public internet, so overlapping them across sites breaks VPNs. When planning, leave room to grow — splitting a /24 into two /25s later is far easier than renumbering a full network.
The IP Subnet Calculator lets you figure out ip subnet calculatorinstantly, without reaching for a spreadsheet or doing the math by hand. Whether you're planning a budget, checking a loan, or working through homework, the tool applies the correct formula behind the scenes and shows the result the moment you enter your numbers.
Unlike a static chart or table, this calculator adapts to your exact inputs. You can adjust any value and see the outcome update in real time, which makes it easy to compare scenarios — for example, "what if the rate were 1% lower?" or "what if I paid an extra $50 a month?"
Common uses: people reach for this tool when they need to find a cidr to subnet mask converter, usable host range calculator, wildcard mask calculator online, or how many hosts in a /24 subnet.
Browser-based tools like this one have a few real advantages over installed software or manual methods:
The IP Subnet Calculator is based on the following formula:
addresses = 2^(32 − prefix) usable hosts = 2^(32 − prefix) − 2
Variables: prefix: CIDR prefix length, the number of network bits (0-32) addresses: total addresses in the subnet (addresses) usable hosts: addresses assignable to devices, excluding network and broadcast (hosts)
For an IPv4 /prefix, the host bits are (32 − prefix). Two addresses are reserved (network and broadcast), so usable hosts are two fewer than the total address count.
Worked example: Step 1: Take a /26 subnet, so prefix = 26. Step 2: Host bits = 32 − 26 = 6. Step 3: Total addresses = 2^6 = 64. Step 4: Usable hosts = 64 − 2 = 62. Result: a /26 subnet holds 64 addresses, 62 usable.
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