CIDR Range Calculator is designed for the exact search intent behind “cidr calculator”. Calculate the network range represented by CIDR notation such as an IPv4 address followed by a prefix length. Calculate the network range represented by CIDR notation such as an IPv4 address followed by a prefix length. How CIDR prefixes work For IPv4, a /n prefix fixes the first n of 32 address bits as the network portion. The remaining 32−n bits vary across the block, giving 2^(32−n) total addresses. Network boundaries The network address is obtained by applying the prefix mask to the address; the last address sets all host bits to 1. Traditional subnet terminology calls that final IPv4 address the broadcast address. Usable hosts are contextual The old “total minus two” shortcut is not universal. /31 point-to-point links and /32 host routes are important exceptions, and cloud platforms can reserve additional addresses. Worked example: A /24 leaves 8 host bits, so the block contains 2^8 = 256 total IPv4 addresses. Common practical uses include Plan IPv4 subnet ranges; Check network boundaries; Convert CIDR prefixes to address counts; Validate firewall or routing ranges. Important limitations: IPv4 and IPv6 have different address sizes and operational conventions. Usable-host counts depend on network context and platform reservations. A CIDR calculator does not test whether an address is actually routed or reachable. Key questions this page should answer include: What does /24 mean in CIDR? For IPv4 it means the first 24 bits are the network prefix, leaving 8 variable bits. How many addresses are in an IPv4 /24? 256 total addresses. How do I calculate the number of IPv4 addresses in a CIDR block? Use 2^(32−prefix length). Are network and broadcast addresses always unusable? No. Modern point-to-point /31 use and host routes are exceptions to the traditional rule. Is CIDR the same as a subnet mask? CIDR prefix length is a compact way to express how many leading mask bits are 1; for IPv4 it maps to a dotted-decimal subnet mask. The page should stay focused on this differentiator: Target CIDR→range intent with exact prefix math and avoid the common 'minus two always' mistake.
How to use this tool
How CIDR prefixes work
For IPv4, a /n prefix fixes the first n of 32 address bits as the network portion. The remaining 32−n bits vary across the block, giving 2^(32−n) total addresses.
Network boundaries
The network address is obtained by applying the prefix mask to the address; the last address sets all host bits to 1. Traditional subnet terminology calls that final IPv4 address the broadcast address.
Usable hosts are contextual
The old “total minus two” shortcut is not universal. /31 point-to-point links and /32 host routes are important exceptions, and cloud platforms can reserve additional addresses.
Examples
IPv4 /24
A /24 leaves 8 host bits, so the block contains 2^8 = 256 total IPv4 addresses.
Common use cases
- Plan IPv4 subnet ranges
- Check network boundaries
- Convert CIDR prefixes to address counts
- Validate firewall or routing ranges
Frequently asked questions
What does /24 mean in CIDR?
For IPv4 it means the first 24 bits are the network prefix, leaving 8 variable bits.
How many addresses are in an IPv4 /24?
256 total addresses.
How do I calculate the number of IPv4 addresses in a CIDR block?
Use 2^(32−prefix length).
Are network and broadcast addresses always unusable?
No. Modern point-to-point /31 use and host routes are exceptions to the traditional rule.
Is CIDR the same as a subnet mask?
CIDR prefix length is a compact way to express how many leading mask bits are 1; for IPv4 it maps to a dotted-decimal subnet mask.