RandoziCIDR Subnet Calculator
Type an IPv4 block such as 192.168.1.0/24 and see its mask, range and usable hosts, then split it into equal smaller subnets. Everything is calculated in your browser.
Network
192.168.1.0/24
254 usable hosts · 256 addresses
- Subnet mask
- 255.255.255.0
- Wildcard mask
- 0.0.0.255
- Network address
- 192.168.1.0
- Broadcast address
- 192.168.1.255
- First host
- 192.168.1.1
- Last host
- 192.168.1.254
- Usable hosts
- 254
- Total addresses
- 256
Split into subnets
4 subnets of /26
| Subnet | Host range | Broadcast | Hosts |
|---|---|---|---|
| 192.168.1.0/26 | 192.168.1.1 – 192.168.1.62 | 192.168.1.63 | 62 |
| 192.168.1.64/26 | 192.168.1.65 – 192.168.1.126 | 192.168.1.127 | 62 |
| 192.168.1.128/26 | 192.168.1.129 – 192.168.1.190 | 192.168.1.191 | 62 |
| 192.168.1.192/26 | 192.168.1.193 – 192.168.1.254 | 192.168.1.255 | 62 |
IPv4 only. Calculated in your browser; nothing you type is sent anywhere.
How it works
- Enter an IPv4 address with its prefix, like 10.0.0.0/16.
- Read the subnet mask, wildcard mask, network and broadcast addresses, first and last host, and number of hosts.
- To split the block, enter a longer prefix (for example 18) in “Split into subnets”.
- Copy a subnet from the list, or the whole list as text.
What people use it for
Plan a network
Carve a /16 office or cloud network into /24 or /26 subnets, one per team or service.
Firewall and routing rules
Get the exact first and last address and the wildcard mask for an access list or security group.
Study for networking exams
Check your own subnetting by hand against the full answer, including /31 and /32 edge cases.
Questions
- How are the values calculated?
- The mask has n leading 1-bits for a /n prefix. The network is the address AND the mask, the broadcast is the network OR the inverted mask (the wildcard). Usable hosts are 2^(32−n) − 2, because the network and broadcast addresses are not assigned to devices.
- What about /31 and /32?
- A /32 is a single address: 1 host, which is the address itself. A /31 has 2 addresses and both are usable (RFC 3021, for point-to-point links), so there is no separate network or broadcast address.
- Does it support IPv6?
- Not yet. This calculator covers IPv4 only. IPv6 blocks are far larger and use a different notation, so they need a separate tool.
- What if my address is not the network address?
- That is fine. 192.168.1.77/24 is accepted and the tool shows the block it belongs to, 192.168.1.0/24. Addresses with leading zeros such as 010.0.0.1 are rejected because they can be read as octal.