// SUBNET CALCULATOR · STUDY TOOLS

Subnet Calculator

IPv4 CIDR inspection and FLSM subnetting. Paste a CIDR like 10.42.67.0/24 to see the network, broadcast, mask, wildcard, host range, and binary representation. Switch to subnet mode to split a parent network into equal-size children by target prefix or by required host count. Useful for VLAN sizing, address plan scoping, and the "do these two ranges overlap" question during commissioning.

CIDR notationExamples: 10.42.67.0/24, 192.168.1.100/27, 172.16.0.0/16
NETWORK
NETWORK ADDRESS
10.42.67.0/24
BROADCAST ADDRESS
10.42.67.255
SUBNET MASK
255.255.255.0
WILDCARD MASK
0.0.0.255
HOSTS
TOTAL ADDRESSES
256
USABLE HOSTS
254
FIRST USABLE
10.42.67.1
LAST USABLE
10.42.67.254
CONTEXT
CLASS
A
SCOPE
RFC 1918 private
BINARY
Network    00001010.00101010.01000011.00000000
Broadcast  00001010.00101010.01000011.11111111
Mask       11111111.11111111.11111111.00000000
Wildcard   00000000.00000000.00000000.11111111
IPv4 only. Runs in the browser, no signups. For VLSM-style mixed-size subnetting, run the subnet operation multiple times against successively smaller children.

When to use this

Sizing a VLAN range and confirming the chosen prefix actually fits the device count.
Sanity-checking an integrator's address plan submittal against the building's projected device load.
Splitting a /16 into /24s for a multi-site rollout and exporting the table for documentation.
Confirming the network and broadcast addresses for an ACL definition.

What it does not do (yet)

IPv6 inspection. VLSM-style mixed-size subnetting in one pass. CSV export. These are on the roadmap. For mixed-size subnetting today, run the subnet operation iteratively against successively smaller children.

Notes

All math runs in the browser and the addresses you enter are not uploaded. Feedback to contact@hans.study.

Related guidance

IP Addressing for Security Integrators, planning subnets and documenting the addressing scheme.
VLAN Segmentation for Physical Security Networks, the segmentation scheme the addresses live inside.
Building a Network for CCTV and Access Control, the deployment context.

Runs in your browser. When you generate output, this site records that a generation happened and the prefix sizes you calculated so I can see which options get used in the field. The text you paste in and the values you enter are not uploaded. See the privacy policy.