Pulsars

CIDR Calculator — IP Subnet Calculator

Examples: 192.168.1.0/24 · 10.0.0.0/8 · 172.16.0.0 255.255.240.0

/24
/0/8/16/24/32

Binary Representation

Private (RFC 1918)Class C
11000000.10101000.00000001.00000000
■ Network (24 bits) ■ Host (8 bits)

Subnet Details

Network Address192.168.1.0/24
Broadcast Address192.168.1.255
Subnet Mask255.255.255.0
Wildcard Mask0.0.0.255
First Usable Host192.168.1.1
Last Usable Host192.168.1.254
Total Addresses256
Usable Hosts254

CIDR (Classless Inter-Domain Routing) notation, defined in RFC 4632, represents IP address ranges as a base address followed by a prefix length (e.g., 192.168.1.0/24). The prefix length indicates how many bits of the address identify the network — a /24 network has 256 addresses (254 usable hosts), while a /16 has 65,536. CIDR replaced the older classful addressing system (Class A/B/C) in 1993 and is fundamental to IP subnetting, routing, and firewall configuration.

How does CIDR notation work?

CIDR replaced the old classful addressing system (Class A/B/C) in 1993. Instead of fixed /8, /16, /24 boundaries, CIDR allows any prefix length from /0 to /32, enabling efficient IP address allocation. A CIDR block like 10.0.0.0/16 means the first 16 bits identify the network, and the remaining 16 bits identify individual hosts within it.

What are the most common subnet sizes?

CIDR Subnet Mask Usable Hosts Typical Use
/32 255.255.255.255 1 Single host, loopback
/30 255.255.255.252 2 Point-to-point links
/24 255.255.255.0 254 Small office, home network
/16 255.255.0.0 65,534 Cloud VPC, campus network
/8 255.0.0.0 16,777,214 Large enterprise (10.0.0.0/8)

How does subnetting differ for cloud providers?

Cloud platforms like AWS, GCP, and Azure reserve additional addresses within each subnet. AWS reserves 5 addresses per subnet (network, broadcast, DNS, future use, and gateway). When planning cloud VPCs, use this calculator to determine available hosts, then subtract the provider's reserved addresses.

Need to debug network patterns? Try our Regex Tester for matching IP address formats, or our Base64 Encoder for encoding network credentials.

Frequently Asked Questions

What is CIDR notation?

+

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its subnet mask as a single expression like 192.168.1.0/24. The number after the slash (prefix length) indicates how many leading bits are the network portion. /24 means the first 24 bits are the network, leaving 8 bits (256 addresses) for hosts.

How do I calculate usable hosts from a CIDR prefix?

+

The formula is 2^(32 - prefix) - 2. You subtract 2 because the first address is the network address and the last is the broadcast address. For example, /24 gives 2^8 - 2 = 254 usable hosts. Exception: /31 and /32 subnets are special cases — /31 has 2 usable addresses (point-to-point links), /32 is a single host.

What is the difference between subnet mask and wildcard mask?

+

They are bitwise inverses of each other. A subnet mask of 255.255.255.0 has a wildcard mask of 0.0.0.255. Subnet masks are used in network configuration (ifconfig, ip addr). Wildcard masks are used in Cisco ACLs and OSPF configurations. Think of the wildcard mask as 'which bits can vary.'

What are RFC 1918 private IP ranges?

+

RFC 1918 defines three private IP address ranges not routable on the public internet: 10.0.0.0/8 (Class A, 16M addresses), 172.16.0.0/12 (Class B, 1M addresses), and 192.168.0.0/16 (Class C, 65K addresses). These are used for internal networks, home routers, VPNs, and cloud VPCs.

What is a broadcast address?

+

The broadcast address is the last address in a subnet. Packets sent to this address are delivered to all hosts on the subnet. It's calculated by setting all host bits to 1. For 192.168.1.0/24, the broadcast is 192.168.1.255. This address cannot be assigned to a device.

Related Tools

🔍
Regex Tester
Test and debug regular expressions in real time. Match highlighting, capture groups, and common presets.
🔣
Base64 Encode / Decode
Encode and decode Base64 strings instantly. Supports standard and URL-safe Base64.