What Is CIDR Notation?

CIDR appends a slash and prefix length to an address. For example, /24 means the first 24 IPv4 bits identify the network and the remaining 8 bits identify addresses within it.

Why Does A /31 Have Two Usable Addresses?

RFC 3021 permits both addresses on an IPv4 /31 point-to-point link, so neither is treated as a traditional network or broadcast endpoint.

Does IPv6 Have A Broadcast Address?

No. IPv6 uses multicast rather than a broadcast address. The calculator therefore shows the first and last addresses in the prefix instead.

IP Subnet Calculator

Inspect IPv4 and IPv6 networks, usable ranges, masks, address counts and smaller subnet plans from CIDR notation.

Network Input

Enter a host address with CIDR, or provide the prefix separately. IPv4 accepts a dotted subnet mask.

IP Address Or CIDRExamples: 192.168.1.42/24 or 2001:db8::1/64.Prefix Or Subnet MaskLeave blank when the address already includes a CIDR prefix.

Address FamilyIPv4

Normalized Address192.168.10.42/24

Input Rules

IPv4 octets must be decimal values from 0 through 255.
Dotted masks must have contiguous network bits, such as 255.255.254.0.
IPv6 supports compressed addresses and embedded IPv4 endings, but not interface zone identifiers.

Calculated Network

The entered host is normalized to its containing network.

Network CIDR192.168.10.0/24IPv4 Network

Address ClassificationPrivate Address

This address is in an RFC 1918 private network and is not globally routed.

Network Address: 192.168.10.0
Broadcast Address: 192.168.10.255
First Usable Address: 192.168.10.1
Last Usable Address: 192.168.10.254
Subnet Mask: 255.255.255.0
Wildcard Mask: 0.0.0.255
Total Addresses: 256
Usable Addresses: 254

Traditional Host NetworkThe network and broadcast addresses are reserved; hosts use the addresses between them.

IPv4 Binary Map

24 Network Bits, 8 Host Bits

Entered Address

Network Address

Subnet Mask

Wildcard Mask

Split This Network

Choose a longer prefix to divide the calculated network into equal-size subnets.

New Prefix

Source Network192.168.10.0/24

Resulting Prefix/26

Total Subnets4

Preview Rows4

Showing all 4 resulting subnets.

Index	Subnet	First Address	Last Address	Address Count	Usable Count
1	`192.168.10.0/26`	`192.168.10.1`	`192.168.10.62`	64	62
2	`192.168.10.64/26`	`192.168.10.65`	`192.168.10.126`	64	62
3	`192.168.10.128/26`	`192.168.10.129`	`192.168.10.190`	64	62
4	`192.168.10.192/26`	`192.168.10.193`	`192.168.10.254`	64	62

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What Is the IP Subnet Calculator?

The IP Subnet Calculator turns an IPv4 or IPv6 address and prefix into a complete network record. For IPv4 it shows the network, broadcast, usable range, subnet mask, wildcard mask and host counts, including the special behavior of /31 and /32 networks. For IPv6 it reports the normalized prefix, full address range and exact address count without inventing a broadcast address.

How It Works

Enter an address in CIDR notation or pair an IPv4 address with a dotted subnet mask. For IPv4, the address ribbon marks network and host bits; the ledger lists the derived values for both address families. To plan a smaller network, choose a longer child prefix and inspect or export the capped range preview. All parsing and calculations run locally in the browser.

When to Use It

Use it while planning a LAN, VLAN, VPN, firewall rule, cloud network, point-to-point link or IPv6 allocation, or when checking whether two addresses belong to the same prefix.

Frequently Asked Questions

What Is CIDR Notation?: CIDR appends a slash and prefix length to an address. For example, /24 means the first 24 IPv4 bits identify the network and the remaining 8 bits identify addresses within it.
Why Does A /31 Have Two Usable Addresses?: RFC 3021 permits both addresses on an IPv4 /31 point-to-point link, so neither is treated as a traditional network or broadcast endpoint.
Does IPv6 Have A Broadcast Address?: No. IPv6 uses multicast rather than a broadcast address. The calculator therefore shows the first and last addresses in the prefix instead.

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