Free Online CIDR Calculator
Enter any CIDR notation to instantly get a full breakdown of network details, including the broadcast address, subnet mask, host range, and IP class. A collection of six specialized tools covers your common networking needs, from expanding CIDR blocks into IP lists to merging overlapping ranges into a minimal set. You can paste your CIDR notation into the input field, upload a file from your computer, or simply drag and drop it onto the workspace. Your addresses stay on your device since all processing happens locally in your browser.
CIDR Calculator
Computes network address, broadcast, subnet mask, wildcard mask, host range, and IP class from any CIDR notation with binary representation.
Subnet Calculator
Calculates the same network details from an IP address and a subnet mask selected from a dropdown with all 33 possible masks.
IP Range
Shows the complete address range for a CIDR block including first and last usable hosts and total address count.
CIDR to IP List
Expands a CIDR block into every individual IP address it contains, displayed in a numbered list with copy and download support.
IP to CIDR
Converts a start and end IP range into the smallest set of CIDR blocks that cover exactly that range with no overlap.
CIDR Merger
Merges overlapping and adjacent CIDR blocks into the minimum number of aggregated blocks for cleaner firewall rules and route tables.
Online CIDR Calculator with Subnet Details and IP Expansion
See your subnet details update instantly as you type your network notation. Just enter a CIDR block like 10.0.0.0/8 and click Calculate to see the full breakdown of network addresses, masks, and host counts. Scan your results easily using the color-coded grid that highlights the most important network values. Binary representations of the subnet mask and network address are also included for those working at the bit level.
Upload CIDR and IP Files
Get your data into the workspace by pasting it directly, dragging and dropping a file, or using the Upload File button. You can work with .txt, .csv, .tsv, and .json files that contain your CIDR blocks or IP addresses. Since everything runs locally using JavaScript, there is no server-side upload limit and your network data never leaves your machine.
Subnet Mask Dropdown for Quick Selection
Quickly select from all 33 possible subnet masks, ranging from /0 to /32, using the dedicated dropdown. Just pick a mask and enter an IP address to see the resulting network details. This approach is often faster when you know the subnet mask but not the prefix length, and it delivers the same comprehensive results as the main calculator.
Expand, Convert, and Merge CIDR Blocks
Beyond basic subnet calculation, you can use three additional tools for more complex CIDR tasks. Expand any CIDR block into a complete list of individual addresses, which you can then copy or download from the numbered panel. For large blocks, the display is limited to the first 1,024 addresses to ensure a smooth experience. If you have a start and end IP range, use the converter to find the smallest possible set of CIDR blocks that cover it exactly.
Merge Overlapping CIDR Ranges
Aggregate multiple CIDR blocks into the smallest possible set by merging overlapping and adjacent ranges. This is perfect for cleaning up firewall rules or route tables that have accumulated redundant entries over time. Each merged block displays its IP range and host count so you can easily verify the results.
Convert IP Ranges to CIDR Notation
Since firewall rules sometimes use start and end IP addresses, our IP-to-CIDR converter helps you find the optimal CIDR representation for any pair. If a single block won't cover the range, the tool generates the smallest set of blocks that covers the space exactly without including extra addresses.
Your Network Data Stays Private in Your Browser
Your privacy is protected since every calculation happens locally in your browser using JavaScript. No network requests are made, no IP addresses are logged, and no data is ever stored on a server. Feel confident using this tool for production network configurations or sensitive internal IP schemes, as your data is never sent anywhere.
Related Networking and Developer Tools
If you work with networks and development tools regularly, these resources complement your CIDR calculations:
- Base64 Encode -- encode data to Base64 for safe transport in URLs and configs
- Base64 Decoder -- decode Base64 strings back to their original format
- UUID Generator -- generate unique identifiers for network devices and configurations
- JSON Formatter -- format, minify, validate, and transform JSON data
- JSON Validator -- validate JSON syntax for API configurations
- JavaScript Preview -- run JavaScript and HTML in a live sandbox with console output
- YAML Validator -- validate YAML files used in network automation