CIDR Calculator – Convert IP Ranges, Find CIDR Blocks, and Split Subnets
About the CIDR Calculator
The CIDR Calculator handles three related networking tasks in one tool: converting a CIDR block into its full IP range, finding the smallest CIDR block that covers a given start and end IP, and splitting a base network into smaller subnets. Switch between the three tabs depending on which direction you’re working, and results update instantly as you type.
It’s built for network engineers and IT students who need more flexibility than a basic subnet lookup, particularly when planning how to divide a larger allocation like a /24 into multiple smaller /26 or /27 subnets. For a simpler single-network breakdown with binary output, the IP Subnet Calculator covers the same core math in a more focused, single-purpose layout.
The Subnet Splitter tab generates a full table of every resulting subnet, including network address, usable host range, and broadcast address, which is useful when documenting a VLAN or DHCP scope plan. Once your ranges are finalized, the DNS Lookup tool is handy for confirming how hostnames resolve within those ranges.
The BigToolSite Team tested all three tabs against manually calculated subnet tables, including odd start/end IP combinations for the range-to-CIDR conversion and large split counts for the subnet splitter, to confirm accuracy across the board.
How to Use the CIDR Calculator
- Select a tab: CIDR to IP Range, IP Range to CIDR, or Subnet Splitter.
- For CIDR to IP Range, enter an IPv4 Address and choose a CIDR Prefix Length to see the full network breakdown.
- For IP Range to CIDR, enter a Start IP Address and End IP Address to find the smallest CIDR block that contains the whole range.
- For Subnet Splitter, enter a Base Network CIDR (e.g., 192.168.1.0/24) and a New Prefix Length larger than the base to divide it into smaller subnets.
- Review the results grid or subnet table for each tab, which update automatically as you edit the inputs.
- Click Reset Inputs to return all three tabs to their default example values.
Example Usage
Tab: Subnet Splitter
Input: Base Network CIDR = 192.168.1.0/24, New Prefix Length = /26
Output: 4 subnets, 62 hosts per subnet: 192.168.1.0/26, 192.168.1.64/26, 192.168.1.128/26, and 192.168.1.192/26, each listed with its first host, last host, and broadcast address.
Switching to the IP Range to CIDR tab with a Start IP of 192.168.1.0 and an End IP of 192.168.1.255 confirms the reverse: the smallest CIDR block covering that exact range is 192.168.1.0/24, containing 256 total IPs.
Frequently Asked Questions
A basic subnet calculator only converts one IP and CIDR at a time, while this tool also finds the smallest CIDR covering an arbitrary IP range and splits a single network into multiple smaller subnets, which are common tasks beyond a single lookup.
CIDR blocks must align to specific binary boundaries, so if your start and end IPs don’t fall on a clean power-of-two boundary, the smallest valid CIDR block that fully contains the range will include some extra addresses outside your original range.
The table renders up to 1,000 subnets directly; if a split produces more than that, the remaining count is summarized in a single row to keep the browser responsive.
This tool performs equal-size splitting only, dividing the base network into subnets of the same new prefix length; unequal or variable-length subnetting (VLSM) across multiple different sizes would need to be done in separate passes.
Yes, it’s fully browser-based with no signup required, and all calculations happen instantly without submitting your data anywhere.
