Subnet Calculator (IPv4 / CIDR)
IPV4 SUBNET CALCULATOR
How to use the subnet calculator
- Type any IPv4 address, such as your router IP 192.168.1.1.
- Pick the subnet mask or CIDR prefix. Most home networks use /24 (255.255.255.0).
- Read the network address, broadcast address, usable host range and number of hosts. Results update as you type.
What is a subnet mask?
A subnet mask splits an IP address into two parts: the network part, shared by every device on the same network, and the host part, unique to each device. On a home network with the mask 255.255.255.0, every device starts with the same first three numbers, such as 192.168.1, and only the last number changes.
What does CIDR notation mean?
CIDR notation writes the mask as a slash and a number, such as /24. The number is how many bits belong to the network part. A /24 network leaves 8 bits for hosts, which gives 256 addresses, of which 254 can be used by devices.
Common subnet masks
| CIDR | Subnet mask | Usable hosts | Typical use |
|---|---|---|---|
| /30 | 255.255.255.252 | 2 | Point-to-point links |
| /29 | 255.255.255.248 | 6 | Small static IP blocks |
| /28 | 255.255.255.240 | 14 | Small office segments |
| /27 | 255.255.255.224 | 30 | Small VLANs |
| /26 | 255.255.255.192 | 62 | Medium VLANs |
| /25 | 255.255.255.128 | 126 | Split home or office network |
| /24 | 255.255.255.0 | 254 | Most home routers |
| /23 | 255.255.254.0 | 510 | Larger offices |
| /22 | 255.255.252.0 | 1,022 | Campus networks |
| /16 | 255.255.0.0 | 65,534 | Large private networks |
Why the network and broadcast addresses are not usable
In most subnets, the first address names the network itself and the last address is the broadcast address, which reaches every device at once. That is why a /24 network has 256 addresses but only 254 usable hosts. The exceptions are /31 point-to-point links and /32 single-host routes.
Worked example: splitting a /24
Say you have 192.168.1.0/24 and want two separate networks, one for staff and one for guests. Enter 192.168.1.0 with /25 in the calculator:
- First network: 192.168.1.0/25, usable 192.168.1.1 to .126.
- Second network: 192.168.1.128/25, usable 192.168.1.129 to .254.
- Each holds 126 devices.
Go one step further with /26 and you get four networks of 62 devices each. The calculator shows the range, broadcast address and host count for each split.
Who uses a subnet calculator
- Students working through networking courses and exams.
- IT staff planning office networks, VLANs and VPNs.
- Home lab users setting up servers, cameras or separate IoT networks.
- Anyone setting a static IP who wants to check the address is in the right range.
Frequently Asked Questions
What subnet mask does my home router use?
Almost all home routers use 255.255.255.0, which is /24. That allows up to 254 devices on the network.
How many hosts are in a /24 subnet?
A /24 subnet has 256 addresses and 254 usable host addresses.
What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. It is used in router access lists and in routing protocols such as OSPF.
Does this calculator support IPv6?
This tool calculates IPv4 subnets. Most home routers still hand out IPv4 addresses inside the private 192.168.x.x or 10.x.x.x ranges.
Last verified: November 2026.