What this IPv4 subnet calculator does
This tool helps you quickly break down any IPv4 address and CIDR prefix into practical subnet details. Enter an address like 192.168.1.130 and a prefix such as /24, and the calculator returns the network address, broadcast address, usable host range, subnet mask, wildcard mask, and host capacity.
If you work in networking, cloud infrastructure, IT support, cybersecurity, or exam prep (Network+, CCNA, etc.), this saves time and reduces errors compared to doing binary math by hand.
How to use it
- Type a valid IPv4 address in dotted decimal format (four octets, 0–255).
- Enter a CIDR prefix from 0 to 32.
- Click Calculate Subnet.
- Review output fields for planning, validation, or troubleshooting.
Quick subnetting concepts (plain English)
IPv4 address
An IPv4 address is 32 bits long, displayed as four decimal octets (for example, 10.0.5.17). Some bits identify the network, while the remaining bits identify hosts on that network.
Subnet mask and CIDR
CIDR notation (like /26) tells you how many leading bits are network bits. That same information can be written as a subnet mask:
- /24 = 255.255.255.0
- /25 = 255.255.255.128
- /26 = 255.255.255.192
- /30 = 255.255.255.252
Network, broadcast, and usable hosts
In most subnets, the first address is the network ID and the last is the broadcast address. Usable hosts typically fall between those two. For common subnetting:
- Usable hosts = total addresses - 2
- Exception: /31 is often used for point-to-point links (2 usable)
- /32 represents exactly one host address
Worked example: 192.168.1.130/24
With /24, the first 24 bits are network bits. That means the subnet spans 192.168.1.0 through 192.168.1.255. Usable host addresses are 192.168.1.1 through 192.168.1.254, giving 254 typical host addresses.
Common CIDR blocks at a glance
- /8 → 16,777,216 total addresses
- /16 → 65,536 total addresses
- /24 → 256 total addresses (254 typical usable)
- /27 → 32 total addresses (30 typical usable)
- /30 → 4 total addresses (2 typical usable)
- /31 → 2 total addresses (point-to-point)
- /32 → 1 total address (single host)
Practical tips
- Always confirm the prefix before assigning static IPs.
- Document gateway, DHCP pools, and reserved ranges clearly.
- Use consistent CIDR blocks to simplify troubleshooting and ACL rules.
- When in doubt, validate the network and broadcast boundaries first.
Final thoughts
Subnetting looks intimidating at first, but once you understand CIDR boundaries, it becomes very mechanical. A reliable IPv4 subnet calculator helps you move faster while staying accurate—especially during migrations, firewall work, VLAN design, and incident response.