Subnet Calculator
Enter an IPv4 address and subnet mask to calculate network information.
Input Information
Supports /xx or 255.255.xxx format
Result
Enter an IP address and subnet mask.
The Subnet Calculator computes the network address, broadcast address, and usable host range from an IPv4 address and subnet mask. It is used in network design, IP allocation planning, and firewall rule configuration.
What is a Subnet Mask?
A subnet mask is a 32-bit value that separates the network and host portions of an IP address. It is expressed in CIDR notation (/24) or dotted-decimal format (255.255.255.0).
- Enter an IP address and CIDR notation, e.g. 192.168.1.0/24.
- Alternatively, select a dotted-decimal mask such as 255.255.255.0.
- The network address, broadcast address, and host range are computed automatically.
- Review the usable host count to understand the size of your network.
192.168.1.0/24
There are 256 total IP addresses (0-255), of which 254 hosts are usable. Ideal for a typical small office network.
10.0.0.0/8
There are 16,777,216 total IP addresses, of which 16,777,214 hosts are usable. Used for large private networks.
192.168.1.0/30
There are 4 total IP addresses with only 2 usable hosts. Ideal for point-to-point links between routers.
Subnet Calculation Formulas
Example
IP: 192.168.1.100 / CIDR: /24
네트워크 주소 = 192.168.1.0
브로드캐스트 = 192.168.1.255
사용 가능: 192.168.1.1 ~ 192.168.1.254
전체 IP: 256, 호스트: 254
CIDR Notation Guide
| CIDR | Mask | Hosts | Use Case |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,214 | Large ISP |
| /16 | 255.255.0.0 | 65,534 | Large enterprise |
| /24 | 255.255.255.0 | 254 | Small office |
| /25 | 255.255.255.128 | 126 | Subnet split |
| /28 | 255.255.255.240 | 14 | Small network |
| /30 | 255.255.255.252 | 2 | P2P link |
Network Design Tips
- Choose the optimal subnet size for the number of hosts to reduce IP waste.
- Network and broadcast addresses cannot be assigned to hosts.
- Subnetting divides a large network into smaller ones.
QWhat is CIDR notation?
CIDR (Classless Inter-Domain Routing) indicates network size with a slash and prefix length. For example, /24 means 24 bits are the network portion.
QHow is the number of usable hosts calculated?
The formula is 2^(32-prefix) - 2. You subtract the network and broadcast addresses from the total number of addresses.
QAre subnet mask and CIDR the same?
They both describe network size but in different formats. A subnet mask uses the form 255.255.255.0, while CIDR uses the form /24.
QDoes it support IPv6?
No. This calculator currently supports IPv4 addresses only. IPv6 uses a 128-bit addressing scheme and requires a separate tool.
QWhy are network and broadcast addresses unusable?
The network address identifies the network itself, and the broadcast address sends messages to all hosts on the network, so neither can be assigned to a host.