CIDR to IP Range Converter
Convert CIDR notation to IP address ranges. Calculate network details, usable hosts, and broadcast addresses instantly.
Working with email systems?
Our API detects disposable and temporary email addresses—protect your signup forms from fake users. Check SPF records or DKIM authentication for your domain.
Get Free API Key →Understanding CIDR Notation
CIDR (Classless Inter-Domain Routing) notation is a compact way to represent IP address ranges. It combines an IP address with a prefix length to define network boundaries.
The Prefix Length
The number after the slash (e.g., /24) indicates how many bits are used for the network portion. A /24 means 24 bits for network, 8 bits for hosts = 256 addresses.
Usable Hosts
In IPv4, the first address is the network address and the last is the broadcast address. A /24 has 256 total IPs but only 254 usable host addresses.
Subnet Masks
The netmask (e.g., 255.255.255.0 for /24) shows which bits identify the network vs. the host. ANDing an IP with the netmask gives the network address.
IPv6 Support
CIDR works with IPv6 too. A /64 is the standard subnet size, providing 18 quintillion addresses per subnet. IPv6 doesn't use broadcast addresses.
Common CIDR Blocks
Quick reference for frequently used IPv4 CIDR notations
| CIDR | Netmask | Total IPs | Usable Hosts | Common Use |
|---|---|---|---|---|
| /32 | 255.255.255.255 | 1 | 1 | Single host |
| /30 | 255.255.255.252 | 4 | 2 | Point-to-point link |
| /28 | 255.255.255.240 | 16 | 14 | Small office |
| /24 | 255.255.255.0 | 256 | 254 | Standard subnet |
| /20 | 255.255.240.0 | 4,096 | 4,094 | Large network |
| /16 | 255.255.0.0 | 65,536 | 65,534 | Enterprise |
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 | ISP / Class A |
CIDR FAQ
Common questions about CIDR notation and IP subnetting
What does the number after the slash mean?
The number after the slash is called the prefix length or network bits. It indicates how many bits (from left to right) are used to identify the network portion of the address. The remaining bits identify individual hosts within that network.
For example, in 192.168.1.0/24, the first 24 bits (192.168.1) identify the network, and the last 8 bits (0-255) can be used for host addresses. More bits for network = smaller network, more bits for hosts = larger network.
Why are there fewer usable hosts than total IPs?
In IPv4 networks, two addresses are reserved for special purposes: the first address (all host bits = 0) is the network address, and the last address (all host bits = 1) is the broadcast address. Neither can be assigned to a device.
For a /24 network (256 total addresses), the usable range is 254 hosts. Exception: /31 networks are used for point-to-point links and have 2 usable addresses, and /32 represents a single host.
What are private IP ranges?
RFC 1918 defines three private IP ranges that aren't routed on the public internet:
10.0.0.0/8 — 16.7 million addresses (Class A private)
172.16.0.0/12 — 1 million addresses (Class B private)
192.168.0.0/16 — 65,536 addresses (Class C private)
These are used for internal networks (home, office, data centers) and require NAT to communicate with the internet. When configuring SPF records, you'll typically use public IP ranges or include directives for your email providers.
How do I calculate subnets manually?
To calculate manually: (1) Convert the prefix to a netmask—for /24, that's 24 ones followed by 8 zeros = 255.255.255.0. (2) AND the IP with the netmask to get the network address. (3) Flip the netmask bits to get the hostmask (0.0.0.255). (4) OR the network address with hostmask to get the broadcast address.
Total hosts = 2^(32 - prefix) for IPv4. Usable hosts = total - 2 (except for /31 and /32).
What's the difference between CIDR and subnet mask?
They represent the same thing differently. CIDR notation /24 is equivalent to subnet mask 255.255.255.0. CIDR is more compact and commonly used in routing tables and cloud configurations. Subnet masks are more common in traditional network device configurations.
CIDR replaced the old classful networking system (Class A/B/C) in 1993, allowing more flexible allocation of IP address space and reducing routing table sizes through aggregation.