Subnet math in the browser, not against a live network

Enter an IPv4 or IPv6 prefix and this planner derives network, broadcast (IPv4), host range, and reverse-DNS labels with integer arithmetic in the page. It does not ping hosts, query WHOIS, or walk a routing table.

IPv4 still reserves network and broadcast addresses in a subnet, so a /24 has 254 usable hosts. IPv6 assignments are usually /64 on a LAN; compressing zeros is display only and does not change the prefix.

Use it to size a VPC, check that two CIDRs overlap, or mint a PTR name before you write the zone file. The result is a calculation, not a guarantee that the addresses are free on the wire.

Network or host

Prefix length /24 · 8 host bits

Specify a prefix if your input omits it.

Quick host fit

Required hosts

Address family

IPv4 IPv6

Ready when you need it.

Validation

Enter a CIDR block to begin.

Network ID

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Prefix —

Address range

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First · Last

Capacity

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Usable hosts

Classification

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Notes

Detailed breakdown

IPv4

Binary & Hex

Expanded

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Bit pattern

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Neighboring Prefixes

Prefix	Mask / hosts	Notes

Subnet Explorer

Split the analyzed block into smaller CIDRs.

Target prefix

CIDR	Range	Usable hosts

Select a prefix to preview subnets.

IP Address Formats

View the network address in multiple formats.

Decimal Dotted

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Binary

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Hexadecimal

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Integer (Decimal)

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IPv4-mapped IPv6

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Reverse DNS (PTR)

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What is CIDR?

Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and IP routing. It replaced the older system based on classes (A, B, and C) to provide more flexibility and efficiency in address distribution.

How to Use This Tool

Enter an IP address with a prefix (e.g., 192.168.1.0/24) or use the slider to adjust the prefix length. Click "Run analysis" to see network details, usable host ranges, and binary representations.

Common Use Cases

Planning network subnets for cloud infrastructure (VPCs), troubleshooting routing issues, calculating host capacity for a given prefix, and converting between CIDR and subnet masks.

Pro Tips

Remember that in IPv4, the first and last addresses in a subnet are typically reserved for the network ID and broadcast address. In IPv6, subnets are almost always /64 for standard local networks.

Common Subnets

CIDR	Subnet Mask	Hosts	Use Case
`/32`	255.255.255.255	1	Single host
`/24`	255.255.255.0	254	Small network
`/16`	255.255.0.0	65,534	Medium network
`/8`	255.0.0.0	16M+	Large network

Private Ranges (RFC 1918)

Range	CIDR	Class
10.0.0.0 – 10.255.255.255	`10.0.0.0/8`	A
172.16.0.0 – 172.31.255.255	`172.16.0.0/12`	B
192.168.0.0 – 192.168.255.255	`192.168.0.0/16`	C

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