IPv4 Subnet Calculator

Calculate IPv4 subnet details and address ranges.

local

❯ subnet/

class C

BIT RULER — 32 BITSnetwork /24host 8 bits

1–8192

9–16168

17–241

25–3210

MASK255.255.255.0

tip: click any bit to set the boundary — network bits identify the subnet, host bits count its addresses

ADDRESS SPACE — INSIDE PARENT 192.168.0.0/16this subnet = 0.39% of parent

192.168.0.0192.168.255.255

NET254 usable hostsBCAST

SPLIT INTO /25 — two halves of 128click a half to drill down

CIDR 192.168.1.0/24SCOPE private · RFC 1918every value is bitwise math — nothing is sent

§01 ABOUT THIS TOOL

Overview

A CIDR calculator that shows the arithmetic rather than just its results. The 32-bit ruler makes the mask boundary something you can see and move: network bits identify the subnet, host bits count its addresses, and the highlighted bit is the boundary itself.

Below it, the address-space bar places the subnet inside its parent block, so “a /26 is one quarter of a /24” stops being a fact you have to memorise.

How to use

Type an IPv4 address, then set the prefix with the −/+ buttons, the MASK slider, or by clicking any bit in the ruler.
Read the result grid — network, first and last host, broadcast, netmask, wildcard, total and usable counts. Click any cell to copy it.
Use the split preview to drill down one level: clicking a half makes it the current subnet, so you can carve a block step by step.

Examples

Carving a /24 for VLANs: set 192.168.1.0/24, then drill down twice to reach four /26 blocks of 62 usable hosts each.
Writing an ACL: copy the WILDCARD value straight into a Cisco access-list or OSPF network statement.
Sizing a link network: set the prefix to /31 and confirm both addresses are usable — no broadcast is reserved.

Notes

The parent block shown in the address-space bar is the next multiple of eight bits above the current prefix — a /26 sits inside its /24, a /24 inside its /16. That matches how address plans are usually written down.

Scope labels come from the registered IANA and RFC allocations (RFC 1918 private space, RFC 6598 CGNAT, RFC 5737 documentation ranges, and so on), evaluated against the network address of the current subnet.

FAQ

Does this send my network data anywhere?

No. The subnet math is bitwise integer arithmetic running entirely in your browser. Nothing is sent to any server, so it is safe to use with internal addressing plans.

Why do /31 and /32 show no subtracted addresses?

Normally two addresses are reserved — the network address and the broadcast address — so usable hosts = total − 2. Per RFC 3021 a /31 point-to-point link uses both addresses, and a /32 is a single host route, so the calculator reports the full count for those prefixes.

What is the wildcard mask for?

It is the bitwise inverse of the netmask (0.0.0.255 for a /24) and is used in Cisco ACLs and OSPF network statements, where a 0 bit means "must match" and a 1 bit means "don't care".

Why is 192.168.01.1 rejected?

A leading zero is ambiguous — historically inet_aton read such an octet as octal, so 010 means 8 rather than 10. That mismatch is a well-known way to slip past address filters, so the tool refuses the ambiguous form instead of guessing which reading you meant.