IP to CIDR Calculator
Convert any IPv4 address range to optimal CIDR notation with our free IP to CIDR Calculator. Enter the start and end IP addresses and instantly get the most specific CIDR block(s) covering the range. Each CIDR block shows the full subnet details: network address, subnet mask, wildcard mask, broadcast address, first and last usable IPs, and host counts. The calculator handles any valid IPv4 range from a single host (/32) to the entire address space, and automatically splits ranges that cross CIDR boundaries into the minimal number of non-overlapping blocks. No signup required.
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Why Use Our IP to CIDR Calculator?
Optimal CIDR Block Generation
The IP to CIDR Calculator uses an efficient algorithm to find the most specific CIDR notation that covers your IP range. It automatically splits the range into the minimal number of non-overlapping CIDR blocks, ensuring each block is as specific as possible. The algorithm handles any valid IPv4 range from a single host (/32) to the entire address space (/0).
Complete Subnet Information
Every CIDR block includes full subnet details: network address, subnet mask, wildcard mask, broadcast address, first and last usable IPs, and host counts. Whether you need a single block or multiple blocks covering a range, each one displays comprehensive information for network configuration and documentation.
Visual Binary Representation
See the binary representation of the network address and subnet mask for each CIDR block. The binary view helps network engineers understand exactly how the prefix length defines the boundary between the network portion and the host portion of the address, making it easy to verify CIDR calculations.
Free & No Signup Required
Calculate CIDR ranges on unlimited IP ranges with no signup, no API key, and no usage limits. All calculations happen entirely in your browser - the IP addresses never leave your device. We do not store, log, or process any data on our servers. Completely free, forever.
Common Use Cases for IP to CIDR Calculation
Network Subnet Planning
Network engineers planning subnets can use the IP to CIDR Calculator to determine the optimal CIDR notation for any IP range. Whether you are designing a new network layout, dividing a large block into smaller subnets, or consolidating multiple ranges, the calculator finds the most specific CIDR blocks with complete subnet details.
Firewall Rule Configuration
Security engineers configuring firewall ACLs often need to specify IP ranges in CIDR notation. The IP to CIDR Calculator converts any start-to-end IP range into the minimal set of CIDR blocks needed, making firewall rules more efficient and easier to manage. Each block includes the wildcard mask needed for Cisco ACL configurations.
Cloud VPC and Subnet Design
Cloud architects designing VPCs on AWS, Azure, or GCP can use the IP to CIDR Calculator to determine the exact CIDR notation for their subnets. The tool helps ensure that subnets do not overlap and that the chosen CIDR blocks provide enough IP addresses for current and future needs.
IP Allocation Documentation
System administrators documenting IP address allocations can use the IP to CIDR Calculator to generate accurate CIDR notation from their IP ranges. The detailed output includes network address, broadcast address, subnet mask, and host counts - everything needed for comprehensive network documentation.
ISP and Data Center Operations
ISPs and data center operators managing large IP blocks need to efficiently allocate address space to customers. The IP to CIDR Calculator helps determine how to split large ranges into smaller CIDR blocks or aggregate multiple ranges into larger blocks for BGP route announcements.
Network Training and Education
Networking students and instructors can use the IP to CIDR Calculator to verify CIDR calculations and understand how IP ranges map to CIDR notation. The binary view feature helps visualize how the subnet mask separates the network and host portions of an address, making it an excellent learning tool.
Understanding IP to CIDR Conversion
What is CIDR Notation?
CIDR (Classless Inter-Domain Routing) notation is a compact way to specify an IP address range using a base address followed by a slash and a prefix length (e.g., 192.168.1.0/24). The prefix length indicates how many bits of the address represent the network portion - the remaining bits identify hosts within that network. For example, /24 means the first 24 bits are the network, leaving 8 bits for hosts, which gives 256 total addresses (192.168.1.0-192.168.1.255). CIDR replaced the older class-based system (Class A, B, C) and allows for much more flexible IP address allocation.
How the IP to CIDR Algorithm Works
- Validate and convert IPs: Both IP addresses are validated for correct IPv4 format (four octets, each 0-255). They are then converted to 32-bit integers for mathematical operations.
- Find the optimal block size: Starting from the first IP, the algorithm calculates the largest possible CIDR block that starts at that address and fits entirely within the remaining range. The block size is constrained by address alignment (the network address must have the right number of trailing zero bits) and the remaining range size.
- Generate details for each block: For each CIDR block, the calculator computes the subnet mask, wildcard mask, broadcast address, first and last usable IPs, and host counts. The algorithm supports all prefix lengths from /0 to /32.
- Repeat until complete: The algorithm moves past the generated block and repeats the process from the next IP address. It continues until the entire range is covered by non-overlapping CIDR blocks.
Understanding CIDR Block Properties
- Network Address: The first address in the block, where all host bits are zero. This identifies the network itself and cannot be assigned to a host.
- Broadcast Address: The last address in the block, where all host bits are one. Used to send packets to all hosts on the network simultaneously.
- Usable Hosts: The addresses between the network and broadcast addresses (total minus 2). For /31 networks (2 IPs), both addresses are usable (no broadcast). For /32, only one address exists.
- Subnet Mask: A 32-bit number where network bits are set to 1 and host bits are set to 0. Used by routers to determine which part of an IP address is the network identifier.
- Wildcard Mask: The inverse of the subnet mask (host bits set to 1). Commonly used in Cisco ACL configurations to specify which bits of an address must match.
Privacy & Security in IP Calculation
The IP to CIDR Calculator processes all data entirely in your browser. The IP addresses you enter and the CIDR calculation results never leave your device. No data is uploaded, stored, or transmitted to any server. This means you can safely calculate CIDR ranges for production networks, internal infrastructure, or customer environments without any data privacy concerns. Because everything runs client-side, there are also no usage limits, no API keys needed, and the tool works even when you are offline after the initial page load.
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Frequently Asked Questions About CIDR Calculation
CIDR (Classless Inter-Domain Routing) notation is a compact way to specify an IP address range. It combines a network address with a prefix length (e.g., 192.168.1.0/24). The prefix length indicates how many bits represent the network portion. For example, /24 means the first 24 bits are the network, leaving 8 bits for hosts, which gives 256 total addresses. CIDR replaced the older class-based system and allows for flexible IP allocation.
Enter a start IP and end IP address, and the calculator finds the optimal set of CIDR blocks that cover the range. It starts from the first IP and finds the largest possible CIDR block that fits, then moves to the next IP after that block and repeats. The algorithm ensures all blocks are non-overlapping and as specific as possible. Each block includes full subnet details: network address, subnet mask, wildcard mask, broadcast address, and host counts.
A /32 CIDR block represents a single IP address. With a prefix length of 32, all bits are network bits and there are zero host bits. This means the block contains exactly one IP address, and it is both the network address and the only usable address. /32 blocks are commonly used in firewall rules to specify individual hosts and in loopback interface configurations.
Not all IP ranges align perfectly with CIDR block boundaries. CIDR blocks require that the network address has the correct number of trailing zero bits for the prefix length. For example, 192.168.1.0/24 covers 192.168.1.0-192.168.1.255, but 192.168.1.100-192.168.1.200 does not align with any single CIDR block. The calculator splits such ranges into the minimal number of non-overlapping blocks.
A /31 block has 2 IP addresses (prefix length 31, leaving 1 host bit). According to RFC 3021, /31 blocks are used for point-to-point links and do not have a separate network and broadcast address - both addresses are usable. A /32 block has only 1 IP address and is used for single hosts. For larger blocks like /24, the first address is the network address, the last is the broadcast address, and the addresses in between are usable by hosts.
A wildcard mask is the inverse of a subnet mask. While a subnet mask has 1s for network bits and 0s for host bits, a wildcard mask has 0s for network bits and 1s for host bits. Wildcard masks are used in Cisco IOS access control lists (ACLs) to specify which parts of an IP address must match. For example, a wildcard mask of 0.0.0.255 with network 192.168.1.0 matches all IPs in the 192.168.1.0/24 range.
Currently, the IP to CIDR Calculator supports IPv4 addresses only. IPv6 uses the same CIDR notation principles but with 128-bit addresses. We recommend using dedicated IPv6 tools for IPv6 subnet calculations. For IPv4, this calculator handles all ranges from a single host (/32) to the entire IPv4 address space (/0).
Yes! The IP to CIDR Calculator is 100% free with no signup, no API key, and no usage limits. Calculate as many IP ranges as you need, as often as you need. All calculations happen entirely in your browser - the IP addresses never leave your device. We do not store, log, or process any data on our servers.