FREE · NETWORK & IT INFRASTRUCTURE
VLSM Subnet Calculator.
Divide an IPv4 block into variable-size subnets from the number of hosts each one needs, with a full allocation table and free space.
- Block size
- 1,024 addresses
- Allocated
- 548 addresses
- Free
- 476 addresses
- Block used
- 53.5 %
- Hosts requested
- 507
- Free blocks
- 192.168.2.36/30, 192.168.2.40/29, 192.168.2.48/28, 192.168.2.64/26, 192.168.2.128/25, 192.168.3.0/24
Allocation plan
| Name | Hosts needed | Subnet | Mask | First host | Last host | Broadcast | Usable | Spare |
|---|---|---|---|---|---|---|---|---|
| Guests Wi-Fi | 250 | 192.168.0.0/24 | 255.255.255.0 | 192.168.0.1 | 192.168.0.254 | 192.168.0.255 | 254 | 4 |
| Sales | 120 | 192.168.1.0/25 | 255.255.255.128 | 192.168.1.1 | 192.168.1.126 | 192.168.1.127 | 126 | 6 |
| Engineering | 60 | 192.168.1.128/26 | 255.255.255.192 | 192.168.1.129 | 192.168.1.190 | 192.168.1.191 | 62 | 2 |
| Voice | 50 | 192.168.1.192/26 | 255.255.255.192 | 192.168.1.193 | 192.168.1.254 | 192.168.1.255 | 62 | 12 |
| Servers | 25 | 192.168.2.0/27 | 255.255.255.224 | 192.168.2.1 | 192.168.2.30 | 192.168.2.31 | 30 | 5 |
| WAN link | 2 | 192.168.2.32/30 | 255.255.255.252 | 192.168.2.33 | 192.168.2.34 | 192.168.2.35 | 2 | 0 |
- Hosts needed should include the gateway and any addresses reserved for routers or HA pairs.
- Every subnet starts on a multiple of its own size, as routing requires.
How to use VLSM Subnet Calculator
Enter the address block, then one line per subnet with its name and the hosts it needs (include the gateway). Download the plan as CSV.
How it works
Each subnet gets the smallest prefix whose usable addresses cover its hosts. Largest subnets are placed first, each aligned on a multiple of its own size, so no address is wasted between them. The remaining space is summarised as CIDR blocks.
Example
192.168.0.0/22 split for 250, 120, 60, 50, 25 and 2 hosts gives /24, /25, /26, /26, /27 and /30 with 476 addresses left.
Questions about VLSM Subnet Calculator
Is VLSM Subnet Calculator free, and do I need an account?
Yes. This tool is free to use in your browser without an account. Processing takes place on your device.
What are the limits and what should I check?
IPv4 only, up to 200 subnets. Subnets that do not fit are listed as such rather than overlapping. Everything is calculated in your browser; nothing is sent or probed on the network. Review the result before using it in your work.
Is my input sent to a server?
Your input is processed in your browser and is not uploaded by this tool. Files and pasted text are cleared when the page is refreshed. Normal website requests are still required to load the page and its libraries. Read the privacy explanation.