Enter an IPv4 address and either a CIDR prefix (like /24) or a subnet mask (255.255.255.0). Click Calculate to get the network address, broadcast address, usable host range, wildcard mask and more. This tool works entirely in your browser and does not send your IP
If you leave both prefix and mask empty you'll be prompted — provide at least one. Use the Example button to load a sample address.
Subnetting is a core networking skill every network engineer, system administrator, and enthusiast should master. At its heart, subnetting divides a single IP network into multiple smaller networks — subnets — allowing better management of IP address space, improved security and reduced broadcast traffic. This Subnet Calculator helps you compute network addresses, broadcast addresses, masks, wildcard masks and usable hosts quickly so you can focus on planning and configuration rather than arithmetic.
IPv4 addresses consist of 32 bits grouped into four octets. The subnet mask determines which portion of the address represents the network and which portion represents hosts. When you provide an IP and a CIDR prefix (for example, /24), the calculator applies the mask, zeroes out the host bits and returns the network address. It also computes the broadcast address — the highest address in the subnet — which is useful to avoid when assigning device IPs.
Why is this important? Suppose you run a small office with multiple departments. Rather than putting every device on a flat network (which can cause unnecessary broadcast traffic and make access control hard), you can create separate subnets for HR, Finance, and Engineering. Subnets make it easier to apply firewall rules, route traffic, and scale address pools.
Understanding the math helps you plan. A /24 subnet has 256 addresses (0–255), 254 of which are typically usable by hosts because one address is reserved for the network and one for broadcast. A /30 has just 4 addresses and is commonly used for point-to-point links where only two hosts are required. Using this calculator, you can immediately see how many addresses a prefix provides and whether it fits your needs.
Another useful concept is the wildcard mask, which is essentially the inverse of the subnet mask. Wildcard masks are heavily used in access control lists (ACLs) and route-maps on many networking devices because they offer a concise way to match ranges of IP addresses. This tool shows the wildcard for your chosen mask so you can paste it directly into your device configuration.
When designing subnets, remember to reserve space for growth. Avoid carving subnets so tightly that you run out of usable addresses when new devices are added. Keep consistent naming and documentation for each subnet: include the network address, mask, gateway IP, DNS servers and purpose. Documentation prevents errors and speeds up troubleshooting.
There are also best practices to follow: use private address ranges (RFC1918) for internal networks, plan DHCP scopes to match your subnets, and apply VLAN tagging at the switch level to keep broadcast domains aligned with logical subnets. For public-facing services, minimize exposure by placing servers behind firewalls and load balancers and only opening the necessary ports.
Finally, practice makes perfect. Use this Subnet Calculator while studying for networking certifications or preparing network diagrams. Try converting between CIDR and mask notation, predict the first and last usable addresses, and verify your assumptions with the tool. Over time the conversions will become second nature and you'll be able to visualize networks quickly.
This Subnet Calculator runs fully in your browser — no external API calls — so it's fast and private. Bookmark it for quick reference, and if you need more advanced features like bulk subnet generation or IPv6 support, check back for future tools on Ipv4chicken.