CIDR to IPv4 Range Calculator
Expand a CIDR block into the full range of addresses it covers, and work the other way too: give a start and end address and get back the smallest set of CIDR blocks that exactly covers the range.
The Subnet / CIDR Calculator works in the other direction, and IPv4 to IPv6 translates a single address.
How to use the CIDR to Range
- 1 Enter a CIDR block such as 10.0.0.0/22 to expand it.
- 2 Read the first and last address, the total size and the number of usable hosts.
- 3 Switch to range mode and enter a start and end address to collapse it into the smallest set of CIDR blocks.
- 4 Copy the resulting block list for a firewall rule or a routing table.
How to Use
In expand mode, enter a block such as 192.168.1.0/24 to see the network address, broadcast address, usable host range, subnet mask and the number of addresses. In collapse mode, enter a start and end address to get the minimal CIDR list — the operation a firewall or router rule needs.
- CIDR to network, broadcast and host range
- Subnet mask, wildcard mask and binary view
- Total and usable address counts
- Range to minimal CIDR block list
- Private, public, loopback and link-local detection
Usable addresses
In the classic subnetting model the first address in a block is the network identifier and the last is the broadcast address, so a /24 has 256 addresses but only 254 that can be assigned to hosts. Point-to-point links with a /31 and loopback /32 blocks are the exceptions, where every address is usable.
Frequently asked questions
What does it mean to collapse an IP range into CIDR blocks?
It expresses a contiguous range as the fewest possible aligned prefix blocks. A range that is not a power-of-two size cannot be one block, so the tool splits it into the minimum set — which is exactly the format firewalls, ACLs and routing tables expect.
Why does 10.0.0.0/22 cover more addresses than I expected?
Because a /22 holds 2^(32−22) = 1024 addresses, not 22. The prefix length is the number of network bits, so a smaller prefix means a bigger block — /24 is 256 addresses and /16 is 65,536.
Why must the network address be aligned?
Because the host bits must all be zero in a valid network address. 10.0.0.0/22 is valid but 10.0.1.0/22 is not — the latter has a host bit set, so tools will normalise it to 10.0.0.0/22, which may cover addresses you did not intend to include.
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