IPv4 Range Calculator
The IPv4 range calculator works in the opposite direction of a subnet calculator: you give it a start and end IP address, and it returns the most efficient set of CIDR blocks that covers the entire range without overlap.
This is useful whenever you have a flat list of addresses (an IP range from a DHCP pool, a block of public IPs from an ISP, or a legacy allocation) and need to express it as clean CIDR notation for routing or documentation. Because CIDR blocks must start on an aligned boundary, a range that is not a power of two is split into the smallest set of blocks that fits.
IPv4 Range Calculator
Find the CIDR notation (or notations) that covers a given IP range.
Enter values above to see results.
Frequently Asked Questions
How do I convert a list of IP addresses into CIDR?
Group the addresses that fall on aligned power-of-two boundaries and express each group as a prefix. The calculator does this for you: enter the first and last address of a range and it returns the smallest set of CIDR blocks that covers every address with no overlap and no wasted space.
What does it mean that an IP range is not CIDR aligned?
A CIDR block always starts on a multiple of its own size, so a range such as 10.0.0.5 to 10.0.0.20 cannot be a single block. The calculator splits it into the fewest aligned blocks that fit, which is why a short range sometimes returns several entries.
Why would I convert an IP range to CIDR?
Routers, firewalls, cloud security groups, and DHCP scopes all expect prefix notation rather than a start and end address. Converting an ISP block or a legacy allocation to CIDR makes it usable in those configurations and keeps your documented plan consistent with the device configuration.
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