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Subnet Calculator with VLSM

Plan IPv4/IPv6 ranges, usable hosts, masks, broadcasts, and right-sized allocations.

What this is

A subnet calculator turns CIDR notation (like /24) into the operational details you actually need: subnet mask, usable host count, network and broadcast addresses, and the wildcard for ACLs. VLSM lets you carve a parent block into right-sized children instead of wasting addresses on uniform splits.

What it covers

  • ›CIDR to mask conversion
  • ›Usable host counts
  • ›VLSM planning
  • ›Reference ranges

Operator notes

  • $Use /30 or /31 for point-to-point links depending on platform support.
  • $Reserve growth space for VLANs that expand often.
  • $Document intent beside every allocation.
status: The calculator UI is next in the tools buildout.

Subnet calculator with VLSM

CIDR:              192.168.0.0/22
Subnet Mask:       255.255.252.0
Wildcard Mask:     0.0.3.255
Network Address:   192.168.0.0
Broadcast Address: 192.168.3.255
First Usable:      192.168.0.1
Last Usable:       192.168.3.254
Total IPs:         1,024
Usable Hosts:      1,022

VLSM breakdown (16 blocks):
/26 192.168.0.1 - 192.168.0.62
/26 192.168.0.65 - 192.168.0.126
/26 192.168.0.129 - 192.168.0.190
/26 192.168.0.193 - 192.168.0.254
/26 192.168.1.1 - 192.168.1.62
/26 192.168.1.65 - 192.168.1.126
/26 192.168.1.129 - 192.168.1.190
/26 192.168.1.193 - 192.168.1.254
/26 192.168.2.1 - 192.168.2.62
/26 192.168.2.65 - 192.168.2.126
/26 192.168.2.129 - 192.168.2.190
/26 192.168.2.193 - 192.168.2.254
/26 192.168.3.1 - 192.168.3.62
/26 192.168.3.65 - 192.168.3.126
/26 192.168.3.129 - 192.168.3.190
/26 192.168.3.193 - 192.168.3.254
/24 = 256 total, 254 usable
/26 = 64 total, 62 usable
/29 = 8 total, 6 usable
/30 = 4 total, 2 usable

Frequently asked

How many usable hosts in a /24?
A /24 has 256 total addresses, minus the network (.0) and broadcast (.255) = 254 usable hosts. The full table is in the subnet cheatsheet.
What's the difference between a subnet mask and a wildcard?
A subnet mask marks the network bits with 1s (255.255.255.0). A wildcard is the bitwise inverse (0.0.0.255) and is what Cisco ACLs use to match host bits.
Can I use /31 between two routers?
Yes — RFC 3021 allows /31 on point-to-point links and both addresses are usable as endpoints. Most modern platforms support it; a few legacy ones still need /30.

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