IPv4 Subnet Calculator

Calculate IPv4 subnet ranges, CIDR blocks, usable hosts, subnet masks, broadcast addresses, and network information instantly.
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Overview

The IPv4 Subnet Calculator takes an IP address and a prefix length and computes the full subnet details instantly. It shows the network, broadcast, usable host range, subnet and wildcard masks, and CIDR notation, plus a visual bar and a binary breakdown of the address. A split table also lists every /prefix subnet inside the containing class block so you can see where your address sits.

Common Use Cases

How to Use

1
Enter the IP address, for example 192.168.1.55.
2
Pick the prefix length from the dropdown; it defaults to /24 and accepts values from 0 to 32.
3
Read the summary badges for CIDR, class, private or public status, and total addresses.
4
Inspect the details table for network address, gateway, broadcast, masks, host range, usable hosts, and CIDR notation, copying any value with its copy button.
5
Scan the subnet split table to see all possible /prefix networks in the containing block; the row for your subnet is highlighted.
6
Watch for the warning alert when a prefix smaller than /8 produces a very large subnet.

Example Scenario

Subnetting 192.168.1.55 with a /24 mask

Enter 192.168.1.55 with prefix 24. The tool reports the network as 192.168.1.0, the broadcast as 192.168.1.255, usable hosts from 192.168.1.1 through 192.168.1.254, the subnet mask 255.255.255.0, and the wildcard mask 0.0.0.255. The split table lists all 256 /24 networks within 192.168.0.0/16 and highlights 192.168.1.0/24.

Technical Notes

The prefix length counts the number of network bits in the subnet mask. A /24 mask is 255.255.255.0, a /16 mask is 255.255.0.0, and a /8 mask is 255.0.0.0. Longer prefixes produce smaller subnets with fewer hosts.

The wildcard mask is the bitwise inverse of the subnet mask, with all host bits set to 1. It is used by routing protocols such as OSPF and by access control lists to match ranges of addresses.

For prefixes below /31, the network and broadcast addresses are reserved, so the usable host count is the subnet size minus 2. For /31 and /32 the calculator reports all addresses as usable because those prefixes are used for point-to-point links and single hosts.

The calculator labels the address with its legacy class, A, B, C, D (Multicast), or E (Reserved), and marks whether the address is in a private range such as 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16.

The split table divides the class boundary one level above the prefix and lists every possible /prefix network. For /25 to /32 it divides a /24, for /17 to /24 a /16, for /9 to /16 a /8, and for smaller prefixes the whole address space.

Common Mistakes

Frequently Asked Questions

It is CIDR notation. The number after the slash is the prefix length, the count of leading bits in the address that are fixed by the subnet mask.

For subnets of /30 or larger, the network address (all host bits zero) and the broadcast address (all host bits one) are reserved and cannot be assigned to hosts.

A subnet mask uses ones for the network part and zeros for the host part, so 255.255.255.0. A wildcard mask is the bitwise inverse, so 0.0.0.255, which matches any host within the subnet.

A prefix of /7 or less, for example, contains tens of millions of addresses. The warning reminds you that splitting such a block into meaningful subnets is usually not practical.

Related Topics

IPv6 Subnet CalculatorIPv4 IPv6 ConverterCIDR notationSubnet maskWildcard mask