CIDR Range Tool
Free ToolResults
What Is This Tool For?
This tool solves two common networking tasks that go beyond a standard subnet calculator:
- CIDR → Range — enter a CIDR block (e.g.
10.0.0.0/22) and instantly see the first IP, last IP, total addresses, and whether the range is private or public. - Range → CIDR — enter any start and end IP address and the tool finds the minimal set of CIDR blocks that exactly covers that range. This is commonly needed when writing firewall rules, BGP route filters, or access control lists.
Why Would an IP Range Need Multiple CIDR Blocks?
CIDR blocks must be power-of-two aligned. A range like 10.0.0.1–10.0.0.6 cannot be expressed as a single CIDR because it is neither aligned nor a power-of-two size. The tool decomposes it into the smallest possible set of aligned blocks — in this case 10.0.0.1/32, 10.0.0.2/31, and 10.0.0.4/30.
Firewall platforms, cloud security groups, and BGP routers all require CIDR notation, so this conversion is frequently needed when you receive an IP range in start–end format.
Understanding Address Counts
- Total addresses — every IP in the block including network and broadcast: 2(32−prefix).
- Usable hosts — subtract 2 from total (network + broadcast are reserved), except /31 (2 usable, RFC 3021) and /32 (1 address, single host).
- Private ranges — 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 (RFC 1918) are non-routable on the public internet.