CIDR to IP Range Converter (and Range to CIDR)
Convert CIDR notation to an IP address range and back: enter 10.0.0.0/22 to get first/last addresses, or enter any start–end range to get the minimal CIDR blocks.
CIDR → range
Range → CIDR blocks
Two converters in one
CIDR to range answers "which addresses does 10.0.0.0/22 actually cover?" — useful when reading firewall rules, allowlists or WHOIS results. Range to CIDR solves the reverse problem: given an arbitrary start and end address, it produces the smallest possible set of CIDR blocks covering exactly that range — handy for building ACLs and route filters from IP ranges published as plain start–end pairs.
Related tools: the subnet calculator for full network details, and WHOIS lookup to see who owns a range.
Frequently asked questions
Why does my range produce several CIDR blocks?
CIDR blocks must be power-of-two sized and aligned. A range like 10.0.0.5–10.0.0.9 doesn't line up with any single block, so the minimal exact cover needs multiple CIDRs.