IP Range to CIDR Converter - Free Online Tool
IP Range to CIDR Converter
Convert Any IP Range to Its Minimal CIDR Blocks
Understanding IP Range Aggregation
Minimal Block Sets
Firewalls and routers often prefer a small number of CIDR blocks over a long list of individual IPs.
Migrating Legacy Rules
Convert an old-style start-end IP range configuration into modern CIDR notation.
Cloud Security Groups
Generate the exact CIDR entries needed to allowlist a specific range of addresses in a security group.
Client-Side Only
All calculation happens locally in your browser — no data is ever sent to a server.
Why a Range Needs Multiple CIDR Blocks
CIDR blocks must start on an address boundary aligned to their prefix length, so an arbitrary IP range rarely maps to a single block. This tool uses the standard aggregation algorithm — repeatedly finding the largest aligned block that fits within what's left of the range — to produce the smallest possible set of CIDR blocks that exactly covers your range.
Key Takeaways
- Minimal Block Count: Uses the standard alignment algorithm to produce the fewest possible CIDR blocks.
- Exact Coverage: The resulting blocks cover your range exactly — no extra addresses included or excluded.
- Client-Side Only: All calculation happens locally in your browser — no data is ever sent to a server.