CIDR & Subnet Calculator

Calculate IPv4 and IPv6 subnets, network boundaries, usable host ranges, and bitwise masks with an interactive subnet planner and routing overlap detector.

CIDR Block or IP Address
RFC 1918

e.g. 10.0.0.0/16 or 192.168.1.0/24

Quick Presets:
Private Network (RFC 1918 Class A)
Class A

Network Address

10.0.0.0

CIDR: 10.0.0.0/16

Broadcast Address

10.0.255.255

Wildcard: 0.0.255.255

Usable Hosts

65,534
/16

Total Addresses: 65,536

Usable Host Range

10.0.0.1 → 10.0.255.254

Mask: 255.255.0.0

IP Scope & Classification

Private Network (RFC 1918 Class A)

Standard: RFC 1918

Interactive Bitwise Representation (32-bit)

16 network prefix bits (highlighted) vs 16 host bits.

Network Address: 10.0.0.0Prefix: /16
00001010
00000000
00000000
00000000
Network Bits (Prefix) (16)
Host Bits (16)
Hexadecimal
0x0A000000
32-bit Integer
167772160
Reverse DNS (PTR Zone)
0.10.in-addr.arpa

How to Use the CIDR Calculator

The CIDR & Subnet Calculator helps cloud architects, DevOps engineers, and SecOps teams plan network topologies without complex manual binary arithmetic.

  1. Input CIDR or IP: Enter any standard CIDR block (e.g. 10.0.0.0/16) or choose from one of the quick presets.
  2. Inspect Detailed Metrics: Review network addresses, broadcast boundaries, RFC classification, and bitwise binary breakdowns.
  3. Plan & Subdivide: Use the Subnet Splitting tab to carve your VPC into micro-subnets and export the allocations to CSV or JSON.
  4. Detect Routing Overlaps: Paste multiple routing tables or security group ranges into the Conflict Detector to prevent routing blackholes.

Frequently Asked Questions (FAQ)

What is CIDR notation?

Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and IP routing. The slash suffix (e.g. /24) indicates the number of leading bits allocated for the network prefix, leaving the remaining bits for host addresses.

Why do /31 subnets have 2 usable hosts instead of 0?

Per RFC 3021, /31 subnets are designated for point-to-point links between routers. Because there are only 2 addresses, the traditional network and broadcast addresses are waived, allowing both addresses to be assigned to the two interface endpoints.

What is the difference between a Subnet Mask and a Wildcard Mask?

A subnet mask uses 1s to match the network portion, while a wildcard mask (used in Cisco ACLs and OSPF) is the bitwise inverse (~mask), using 1s to indicate 'don't care' host bits.

Is my network data private?

Yes. All calculations, bitwise operations, and overlap analyses execute entirely inside your web browser. No network requests or IP configurations are ever sent to our servers.

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