IP Range to CIDR Calculator
Use this IP range to CIDR calculator when a vendor, firewall, allowlist, or route table needs CIDR blocks instead of a start and end IPv4 range.
Calculator
How to use this calculator
Enter the planning values that match your network, storage, or cloud scenario. Use realistic production assumptions when sizing anything that affects availability, performance, or cost.
Formula or calculation method
The range is walked from the first address to the last address. At each step, the calculator chooses the largest aligned CIDR block that fits inside the remaining range.
Worked example
A range from 192.168.10.20 to 192.168.10.90 becomes several CIDR blocks because the start and end do not align on one clean subnet boundary.
Practical planning tips
- Firewall allowlists.
- Cloud security group rules.
- Route summaries for small address ranges.
Common mistakes to avoid
- Entering the end address before the start address.
- Assuming every range can be represented by one CIDR block.
- Mixing public and private ranges without checking policy.
Frequently asked questions
Why are there multiple blocks?
CIDR blocks must align on binary boundaries, so irregular ranges often need several blocks.
Does this support IPv6?
No. This page converts IPv4 ranges only.