IPv4 Subnet Calculator
Enter an IPv4 address and CIDR prefix to calculate network details instantly.
Why use an IPv4 calculator?
Subnetting is one of those skills that feels tricky at first and obvious later. An IPv4 calculator helps you move from guesswork to precision by turning an address and prefix into practical network information you can use right away. Whether you are planning VLANs, validating firewall rules, assigning static hosts, or documenting infrastructure, you need exact values for network address, broadcast address, and host range.
Manual subnet math is absolutely worth learning, but when speed and accuracy matter, a calculator avoids mistakes and saves time. The tool above is designed for day-to-day networking tasks: clean input, immediate feedback, and output in the same terms network engineers use.
What this IPv4 calculator gives you
Once you enter an IP address and CIDR prefix, the calculator returns:
- Network address (the subnet identifier)
- Broadcast address (last address in the subnet)
- First and last usable host (when applicable)
- Total addresses and usable hosts
- Subnet mask and wildcard mask
- Binary forms for IP and mask
- Address class and type (public/private/special-use)
How to use it correctly
Step 1: Enter a valid IPv4 address
Use standard dotted-decimal notation such as 10.0.3.17 or 172.16.20.200. You can also paste CIDR directly in the IP field, like 192.168.1.50/24.
Step 2: Enter a prefix length
Prefixes range from /0 to /32. If you entered a CIDR suffix in the IP field, this tool will automatically use it.
Step 3: Click Calculate
The result panel shows all subnet information in one place. If input is invalid, the calculator displays a specific error message so you can fix it quickly.
Quick CIDR reference
- /8 → mask 255.0.0.0
- /16 → mask 255.255.0.0
- /24 → mask 255.255.255.0
- /30 → 4 addresses (2 usable in classic subnetting)
- /31 → 2 addresses (commonly point-to-point links)
- /32 → single host route
Example subnet walkthrough
Example: 192.168.10.34/24
With a /24, the subnet mask is 255.255.255.0. The network becomes 192.168.10.0, and broadcast is 192.168.10.255. Usable host range is 192.168.10.1 through 192.168.10.254. That gives you 256 total addresses, 254 usable in standard host allocation.
Example: 10.14.8.9/20
A /20 means the mask is 255.255.240.0. Subnets increment by 16 in the third octet. Since 8 falls in the 0–15 block, the network is 10.14.0.0 and broadcast is 10.14.15.255. This subnet has 4096 total addresses and 4094 usable.
Common subnetting mistakes to avoid
- Confusing network address with first usable host.
- Forgetting that /31 and /32 behave differently from typical LAN subnets.
- Mixing wildcard mask and subnet mask in ACL configurations.
- Using overlapping CIDR blocks across routed segments.
- Assuming private address means secure—routing and firewall policy still matter.
When this tool is most useful
This IPv4 subnet calculator is ideal for network design sessions, change windows, incident response, and certification study. It is also helpful for cloud planning, especially when splitting VPC/VNet blocks and validating non-overlapping CIDR allocations.
Keep this page bookmarked if you regularly work with routing tables, DHCP scopes, ACL entries, VPN tunnels, or any scenario where one off-by-one error can break connectivity.