CIDR / Subnet Calculator

Calculate network details from any IPv4 CIDR block. All calculations run instantly in your browser.

Network Address

192.168.1.0

Broadcast Address

192.168.1.255

Subnet Mask

255.255.255.0

Wildcard Mask

0.0.0.255

First Usable IP

192.168.1.1

Last Usable IP

192.168.1.254

Total Hosts

256

Usable Hosts

254

IP Class

Private Address

Yes

Prefix Length

/24

Binary Mask

11111111111111111111111100000000

About This Tool

CIDR replaced the original classful addressing system (Class A/B/C) in 1993 with RFC 1519. Instead of being limited to fixed /8, /16, or /24 boundaries, network administrators can allocate address space in any power-of-two block from /0 to /32. This dramatically improved IPv4 address utilization and slowed the exhaustion of the IPv4 address space.

When planning a network, choosing the right prefix length is critical. A /24 gives 254 usable addresses, suitable for a small office LAN. A /28 provides 14 usable addresses, ideal for a DMZ or a small server VLAN. Point-to-point links between routers typically use /30 (2 usable addresses) or /31 (RFC 3021 allows 2 addresses with no broadcast). Cloud providers like AWS use /16 VPCs by default, giving you 65,534 usable IPs to subdivide across subnets and availability zones.

Supernetting (route aggregation) is the reverse process: combining multiple smaller subnets into a single larger CIDR block to reduce the size of routing tables. For example, four contiguous /24 networks can be summarized as a single /22. This is essential for BGP route announcements and keeping the global routing table manageable.

Frequently Asked Questions

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation is a compact way to describe an IP address and its associated network mask. It is written as an IP address followed by a slash and a number (e.g., 192.168.1.0/24). The number after the slash indicates how many bits of the address are used for the network portion.

How do I calculate the number of hosts in a subnet?

The number of total hosts in a subnet is 2^(32 - prefix length). For example, a /24 network has 2^8 = 256 total addresses. The number of usable hosts is total hosts minus 2 (one for the network address and one for the broadcast address), so a /24 has 254 usable hosts.

What is a subnet mask?

A subnet mask is a 32-bit number that separates the network portion of an IP address from the host portion. In dotted decimal notation, a /24 prefix corresponds to 255.255.255.0. Every bit set to 1 in the mask belongs to the network, and every bit set to 0 belongs to hosts.

What is a wildcard mask?

A wildcard mask is the bitwise inverse of a subnet mask. It is commonly used in access control lists (ACLs) on Cisco routers and in OSPF area configurations. For a /24 subnet (mask 255.255.255.0), the wildcard mask is 0.0.0.255.

What are private IP address ranges?

RFC 1918 defines three private IPv4 address ranges: 10.0.0.0/8 (10.0.0.0 – 10.255.255.255), 172.16.0.0/12 (172.16.0.0 – 172.31.255.255), and 192.168.0.0/16 (192.168.0.0 – 192.168.255.255). These addresses are not routable on the public internet.