VLSM Subnet Planner

Right-sized subnets packed efficiently from a list of host requirements

1. Address Pool

Enter the network to carve up. This is the same calculator as the IPv4 Calculator page — a compact copy lives here so the planner works on its own.

IP Address (optionally with /CIDR)

Subnet Mask (if no /CIDR above)

2. Subnet Requirements

Uses the pool above. Enter one requirement per line as Name,HostsNeeded (e.g. Sales,50) or just a number — subnets are sized to the smallest block that fits and packed efficiently, largest first.

Subnet requirements

Name	Hosts Needed	CIDR	Network	Usable Range	Broadcast	Usable Hosts

How VLSM differs from a plain split

The Subnet Splitter divides a network into equal-sized pieces. VLSM (Variable-Length Subnet Masking) instead sizes each subnet to what it actually needs, then packs them into the pool largest-first so the address space isn't wasted on undersized requirements getting an oversized block.

Example: a department needing 50 hosts gets a /26 (64 addresses, 62 usable), while one needing 5 hosts gets a /29 (8 addresses, 6 usable) — instead of every department being forced onto the same fixed prefix.