CIDR Range Calculator
Expand a CIDR block into its address range, check whether an address is inside it, or compare two addresses.
Runs entirely in your browser — nothing is sent anywhere
What each mode does
Expand a range
Turns a CIDR block into its first address, last address and exact size. Useful when you need to write a firewall rule, reserve a DHCP pool or check that two allocations do not overlap.
Is an IP inside?
Answers whether one address falls within a block — the question behind “does this access rule actually match that client?”.
Same network?
Answers whether two addresses share a network at a chosen prefix length. This is the check behind “can these two hosts talk directly, or does traffic have to cross a router?”. It also reports the smallest single block that covers both addresses.
CIDR in one paragraph
CIDR notation writes a block of addresses as an address followed by a prefix length: 192.168.1.0/24. The prefix length counts how many leading bits are fixed. Everything below that boundary is free to vary, so a /24 covers 256 IPv4 addresses, a /25 covers 128, and so on. The same notation works for IPv6, where the address is 128 bits, so a /64 — the usual size of a single network — contains about 18 quintillion addresses.
Limitations
- This tool works with a single block at a time. Aggregating or subtracting lists of blocks is not part of this release.
- For IPv4 subnetting detail — masks, wildcard masks, usable host counts and the binary view — use the subnet calculator.
What does the number after the slash mean?
It is the prefix length: how many leading bits of the address identify the network. A /24 fixes the first 24 bits and leaves 8 for hosts, which is 256 addresses. Each step down the prefix doubles the block size.
Why did my block change when I pressed calculate?
A CIDR block is identified by its network address, so any host bits are cleared. 192.168.1.130/24 describes the same block as 192.168.1.0/24. MyIPKit tells you when this happened rather than changing your input silently.
Does this work with IPv6?
Yes. Expanding a range, checking containment and comparing two addresses all work for IPv6 as well as IPv4. Counts for large IPv6 blocks are computed exactly rather than approximated.