What does a CIDR prefix like /24 mean?

The prefix is how many bits from the left are the network portion. /24 means the first 24 bits are fixed (the network) and the remaining 8 bits address hosts, giving 256 addresses.

Why are usable hosts two fewer than total addresses?

In a normal subnet the first address is the network identifier and the last is the broadcast address, so they cannot be assigned to hosts. /31 and /32 are special cases used for point-to-point links and single hosts.

How many addresses are in a /24?

A /24 contains 256 total addresses (2^8) with 254 usable hosts, because the network and broadcast addresses are reserved. A /22 has 1,024 total and 1,022 usable.

What subnet mask does /24 correspond to?

/24 maps to the subnet mask 255.255.255.0. The prefix sets that many leading bits to 1, so /16 is 255.255.0.0 and /28 is 255.255.255.240.

Is any data sent to a server?

No. All bitwise maths runs in your browser; nothing about the block is transmitted.

CIDR to IP Range — Gera Tools

CIDR (Classless Inter-Domain Routing) notation compresses an IP range into an address and a prefix, like 192.168.1.0/24. This tool expands any IPv4 CIDR block into its full details: the network address, broadcast address, usable host range, subnet mask, and the total and usable address counts. It is built for network engineers planning subnets and anyone decoding a firewall or routing rule.

How it works

The prefix is the number of leading bits that form the network portion; the rest address hosts. The tool converts the IP to a 32-bit integer, builds a mask with the top prefix bits set, then derives:

Network = IP AND mask (the lowest address in the block)
Broadcast = network OR (NOT mask) (the highest address)
Total addresses = 2^(32 − prefix)
Usable hosts = total − 2, since the network and broadcast addresses are reserved

/31 (point-to-point links) and /32 (single host) are special cases with 2 and 1 usable addresses respectively.

Example

For 192.168.1.0/24:

Field	Value
Network	192.168.1.0
Broadcast	192.168.1.255
Subnet mask	255.255.255.0
Usable range	192.168.1.1 – 192.168.1.254
Total / usable	256 / 254

All calculations are bitwise integer maths performed locally in your browser.