CIDR calculator
Paste any IPv4 CIDR block to expand it into its first and last address, subnet mask, and host count. Everything is computed in your browser as you type.
Type any IPv4 CIDR block to expand it into its full address range.
From a CIDR block to a full range
A CIDR block like 203.0.113.0/24 is shorthand for a contiguous range of addresses. The prefix, /24 here, marks how many leading bits are fixed; the rest are free to count through every host. This calculator turns that shorthand into the concrete first address, last address, and total count, which is exactly what you need when writing a firewall rule or a route.
The most common question it answers is "what IP range does this CIDR cover?" The answer is the network address (all host bits zero) through the broadcast address (all host bits one). For a deeper walkthrough, read what is CIDR, or grab the full CIDR cheat sheet for every prefix at a glance.
Frequently asked questions
How do I convert a CIDR block to an IP range?
Set every host bit to 0 for the first address and to 1 for the last. For 203.0.113.0/24 that is 203.0.113.0 to 203.0.113.255. The calculator does it as you type.
What is CIDR notation?
CIDR notation writes a network as an address plus a prefix length, like 10.0.0.0/8. The prefix says how many leading bits identify the network. See the full guide on what CIDR is.
How many addresses are in a CIDR block?
It is 2 to the power of the host bits. A /24 has 8 host bits, so 256 addresses. A /22 has 10 host bits, so 1,024. The calculator shows both the total and the usable host count.
What is the difference between a CIDR block and a subnet?
None, in practice. A CIDR block is a range described by a prefix, and a subnet is a block created by dividing a larger one. Both are the same kind of object.