IP
VLSM Subnet Calculator
Give each segment a name and a host count; the full range for each subnet is calculated for you.
1
Which network do you want to split?
Write the network prefix in slash notation — e.g. 192.168.1.0/24
2
How many subnets do you need?
Enter a number and click "Apply" to set how many rows step 3 has.
3
Name and host count for each subnet
In the right-hand column, enter the segment name (e.g. "Sales"), and in the next column, the number of hosts that segment needs.
Subnet name
Host count
| # | Subnet name | Hosts needed | Network address | CIDR | Subnet mask | First host | Last host | Broadcast | Usable capacity | Wasted |
|---|
Prefix
or mask
Allocation uses the standard VLSM method: the largest subnets are placed first so the least space is wasted. Every subnet sets aside two addresses for the network ID and broadcast, so a segment with 50 hosts needs a
/26 block. To inspect a single CIDR block, use CIDR Calculator.
ABOUT
VLSM calculator: split a network into named subnets
With VLSM each segment gets as many addresses as it needs instead of one fixed size. You give a name and the required host count for each segment (for example “servers”, “management”, “guest Wi-Fi”); the tool places the largest first, builds the full range of each subnet and avoids wasting addresses.
HOW TO
How to use it
- Enter the parent network as CIDR.
- Add each segment with its name and required hosts.
- A table with range, mask and broadcast per subnet is generated — copy it.
FAQ
Frequently asked questions
Why is the largest subnet placed first?
Large blocks must sit on aligned boundaries; allocating from large to small minimises wasted space.
What if there is not enough room?
The tool warns that the parent network cannot hold the total demand and you need a shorter prefix (a bigger network).