Subnet/CIDR Calculator
Calculate network address, broadcast address, usable hosts and more from any IP/CIDR input.
How it works
This calculator takes an IP address in CIDR notation (e.g. 10.0.0.0/16) and
performs bitwise operations to determine the network boundaries. The CIDR prefix length
defines how many bits of the address are used for the network portion; the remaining
bits identify hosts within that network.
Key terms
- Network Address
- The first address in the subnet, identifying the network itself. Not assignable to a host.
- Broadcast Address
- The last address in the subnet, used to send packets to all hosts on the network. Not assignable to a host.
- Subnet Mask
- A 32-bit mask that separates the network portion from the host portion of an address. For example, /24 produces 255.255.255.0.
- Wildcard Mask
- The inverse of the subnet mask. Used in ACLs and OSPF configurations. A /24 wildcard is 0.0.0.255.
- Usable Hosts
- Total addresses minus the network and broadcast addresses. A /24 has 256 total addresses but 254 usable hosts. Exception: /31 networks (RFC 3021) use both addresses for point-to-point links.
How to use this tool
Enter any IP address followed by a CIDR prefix length in the input field (e.g.
10.0.0.0/16 or 192.168.1.50/24). The calculator instantly
shows the network boundaries, usable host range, and all related values. You can
enter any address within the subnet, not just the network address. The tool will
determine the correct network address automatically.
Common subnet sizes
| CIDR | Subnet Mask | Total Addresses | Usable Hosts | Typical Use |
|---|---|---|---|---|
| /30 | 255.255.255.252 | 4 | 2 | Point-to-point links between routers |
| /28 | 255.255.255.240 | 16 | 14 | Small DMZs, management networks |
| /27 | 255.255.255.224 | 32 | 30 | Server VLANs, small departments |
| /26 | 255.255.255.192 | 64 | 62 | Medium VLANs, branch offices |
| /25 | 255.255.255.128 | 128 | 126 | Larger VLANs, floor networks |
| /24 | 255.255.255.0 | 256 | 254 | Standard LAN subnet (most common) |
| /22 | 255.255.252.0 | 1,024 | 1,022 | Large office floors, Wi-Fi networks |
| /20 | 255.255.240.0 | 4,096 | 4,094 | Campus networks, cloud VPCs |
| /16 | 255.255.0.0 | 65,536 | 65,534 | Large enterprise networks, 172.16.x.x ranges |
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 | 10.x.x.x private space |
Subnetting in practice
Splitting a network into smaller subnets
Subnetting divides a larger network into smaller, more manageable segments. For example,
if you have 10.1.0.0/16 and need four equal subnets, increase the prefix
by 2 bits (since 22 = 4):
10.1.0.0/18(10.1.0.1 to 10.1.63.254)10.1.64.0/18(10.1.64.1 to 10.1.127.254)10.1.128.0/18(10.1.128.1 to 10.1.191.254)10.1.192.0/18(10.1.192.1 to 10.1.255.254)
Right-sizing your subnets
Choose a prefix length based on the number of devices you expect, plus room for growth. A good rule of thumb is to plan for 2x your current device count. If a VLAN has 40 devices today and might grow to 80, a /25 (126 usable hosts) gives comfortable headroom, while a /26 (62 usable) would be too tight.
Avoid making subnets unnecessarily large. A /16 for a 50-device network wastes address space and creates an oversized broadcast domain that degrades performance. Conversely, subnets that are too small force frequent re-addressing as the network grows.
Special prefix lengths
- /31 (2 addresses)
- RFC 3021 allows /31 subnets for point-to-point links. Both addresses are usable since there is no need for a network or broadcast address on a two-device link. Saves address space on WAN links.
- /32 (1 address)
- Represents a single host. Used in routing tables to create a host route, in firewall rules to match a specific IP, and in loopback interface configurations on routers.