Subnet Calculator
Enter an IPv4 address and CIDR prefix to calculate subnet details, then optionally split the block into equal subnets.
IPv4 Subnet Calculator
What Is Subnetting?
Subnetting divides a larger IP network into smaller, more manageable segments called subnets. Every IPv4 address is a 32-bit number split into two parts. The network portion identifies the subnet itself, and the host portion identifies individual devices within it. A subnet mask determines where that boundary falls. Subnetting is essential for efficient network design. It reduces broadcast traffic, improves security through logical segmentation, and makes the best use of limited IPv4 address space. The skill applies whether you are configuring a home router, planning a corporate campus network, or provisioning cloud infrastructure. For a step-by-step introduction, see our subnetting beginner’s guide.
Understanding CIDR Notation
Classless Inter-Domain Routing (CIDR) replaced the older classful addressing system in 1993. It remains the standard way to describe IP subnets today. A CIDR notation like 192.168.1.0/24 pairs an IP address with a prefix length. The prefix tells you how many leading bits belong to the network. A /24 means the first 24 bits are the network portion. That leaves 8 bits for host addresses, which gives 256 total addresses and 254 usable. This calculator converts any prefix from /0 through /32. It returns the subnet mask, wildcard mask, network address, broadcast address, and usable host range. You can type the prefix into the IP field as CIDR (192.168.1.0/24), or pick it from the dropdown. Do you only need the explicit first-to-last IP range for an allowlist or firewall rule? Use the CIDR to IP Range Converter. To see the binary math behind each octet, try the IP Binary Converter.
Practical Subnetting Examples
Consider a common scenario. You have been assigned the 10.0.0.0/24 block and need to split it among four departments. This calculator’s split planner shows that four equal subnets require a /26 prefix. Each department gets 64 total addresses and 62 usable hosts. The resulting subnets are 10.0.0.0/26, 10.0.0.64/26, 10.0.0.128/26, and 10.0.0.192/26. If one department needs more hosts, allocate a /25 (126 usable) to it. Then split the remaining /25 into two /26 blocks. This variable-length subnet masking (VLSM) is a direct benefit of CIDR-based subnetting.
When to Use This Tool
Use this subnet calculator to verify network boundaries before configuring routers, firewalls, or DHCP scopes. It is equally useful for exam preparation, troubleshooting connectivity issues, or auditing existing address plans. Enter any valid IPv4 address, select a prefix, and the tool returns the full details. That includes the wildcard mask required for access control lists in Cisco IOS and similar platforms. The results also flag the AWS-usable count, since cloud subnets reserve more than the usual two addresses. Understanding IPv4 and IPv6 and recognizing public vs. private ranges will help you plan allocations effectively.
Frequently Asked Questions
How many usable hosts are in a /26 subnet?
A /26 has 64 total addresses and 62 usable hosts. The network and broadcast addresses are reserved, which removes two. In an AWS VPC subnet the usable count drops to 59. AWS reserves the first four addresses and the last one.
What is the difference between a subnet mask and a wildcard mask?
A subnet mask marks the network bits as 1 and the host bits as 0, so a /24 is 255.255.255.0. A wildcard mask is its exact inverse, 0.0.0.255 for a /24. Cisco access control lists and OSPF statements use the wildcard form.
How do I split a network into smaller subnets?
Add bits to the prefix. Each extra bit doubles the number of subnets and halves their size. Splitting a /24 into four equal parts needs two more bits, giving four /26 blocks of 62 usable hosts each. The split planner in this tool does the division for you.
Related Tools & Resources
Explore more of our free networking tools. Expand a CIDR block with the CIDR to IP Range Converter, or look up DNS records. You can also find your public IP address or identify hardware with the MAC Address Lookup. Another option is to check which services use which network ports.