Planning
VLSM calculator — plan subnets by host requirements
Enter an IPv4 network and the host count for each subnet. Get a VLSM plan with masks, address ranges and allocation explained.
New to this tool? Start here.
Click an example below the form. Look at the result, then change one value to compare what happens.
- VLSM
- Splitting one network into differently sized subnets. A small office can receive fewer addresses than a large department.
- Host
- A device that needs its own address, such as a computer, phone or printer. Enter the device count and the tool chooses the subnet size.
01 / Input
Start with your data
Your data is processed in the browser. Sharing a result is your choice.
02 / Your result
A result you can understand.
Fill in the form or choose an example. You will see the values and how they were calculated.
02 / Your result
Step by step
How did we get here?
How to use it
Enter a parent network and host requirements. Larger subnets are allocated first. Each allocation reserves its network and broadcast addresses.
A little network lab
An office, servers and guests inside one /24
You have 192.168.10.0/24 and need subnets for 50, 20 and 10 host addresses. These requirements include gateway interfaces; the calculator does not add them separately.
A /27 provides only 30 usable hosts, too few for 50. A /26 provides 62, so the first allocation is 192.168.10.0/26.
20 hosts fit in a /27. The next free, correctly aligned block begins at 192.168.10.64 and ends at .95.
10 hosts fit in a /28: network .96, hosts .97–.110 and broadcast .111. The rest of the /24 remains available.
Your turn
What is the smallest ordinary subnet for 63 hosts?
Show answer and explanation
A /25: 128 addresses, including 126 usable hosts. A /26 has only 62 usable hosts and is too small.
Official documents
Standards & sources
Sources checked:
The date refers to checking the listed documents and registries, not endorsement by their authors. Calculation assumptions and limits appear with the result. How we prepare the material.