IPv6 / CIDR Calculator
A pure front-end IPv6 network calculator that performs 128-bit address arithmetic using the browser’s native BigInt. It offers five core features: prefix calculation, subnetting by subnet count, address compression/expansion, base conversion, and address type detection. IPv6 only — for IPv4 calculations please use IP Calculator。
IPv6 / Prefix calculation
Split by number of subnets
Address compress / expand
Base / format conversion
Address type detection
IPv6 / CIDR CalculatorUser Guide
IPv6/CIDR address calculator is a practical tool for network engineers and developers working with IPv6 addresses, offering five core features: prefix calculation, CIDR subnetting, address compression/expansion, base conversion, and address type detection. All calculations use the browser’s native BigInt to perform 128-bit arithmetic, running entirely in the browser without uploading any data。
Key features
🌐 IPv6 / Prefix calculation
Enter an IPv6 address and prefix length to automatically calculate the network prefix, the first and last addresses of the range, and the total address count。
Input:
2001:db8::/32Network prefix：
2001:db8::Start address：
2001:db8::End address：
2001:db8:ffff:ffff:ffff:ffff:ffff:ffffTotal addresses：
2^96
📊 Split by number of subnets
Given a prefix, derive the new prefix length from the desired number of subnets and list each subnet prefix。
Base prefix：
2001:db8::/32Subnet count：
16New prefix：
/36Addresses per subnet：
2^92Subnet example：
2001:db8::/36、2001:db8:1000::/36 …
🔄 Address compress / expand
On :: Converts between the zero-compressed form and the full 8-group form, following the RFC 5952 standard。
intact：
2001:0db8:0000:0000:0000:0000:0000:0001Compress：
2001:db8::1
🔢 Base / format conversion
Converts an IPv6 address into multiple formats including 128-bit binary, a decimal big integer, and hexadecimal。
Address：
2001:db8::1Decimal：
42540766411282592856903984951653826561Hex:
0x20010db8000000000000000000000001
🛡️ Address type detection
Automatically determines an IPv6 address’s class (global unicast, link-local, unique local, multicast, loopback, etc.) and whether it is routable。
Address：
fe80::1Class：
Link-localRange：
fe80::/10Routable：
No
How to use
Select a calculation
Choose prefix calculation, subnetting, address compression/expansion, base conversion, or address type detection as needed. Each feature has its own input area and calculate button。
Enter an IPv6 address or prefix
Enter the IPv6 address, prefix length, or subnet count in the corresponding field. Both compressed and full address notations are supported, and the tool validates the format automatically。
View results
After you click Calculate, results are shown in a clear format, with very large values given both as a power of 2 and as the full number. Every result item can be copied with one click。
IPv6 Address basics
IPv6（Internet Protocol version 6）is the next-generation Internet Protocol, using 128-bit address (IPv4 is 32-bit). The total address space is about 3.4×10³⁸ addresses, fundamentally solving the IPv4 address exhaustion problem. An address consists of 8 groups of 4 hexadecimal digits each, separated by colons。
Address notation
Full form
8 groups of 4 hex digits each written out in full, e.g. 2001:0db8:0000:0000:0000:0000:0000:0001。
Leading-zero omission
Leading zeros in each group can be omitted, e.g. 0db8 written as db8、0000 written as 0。
Double-colon compression
The longest run of consecutive zero groups can use :: and may appear only once in an address, e.g. 2001:db8::1。
Prefix notation
Use Address/prefix length denotes a network, e.g. 2001:db8::/32，Prefix length value 0–128。
Address types explained
Global unicast (2000::/3)
Publicly routable
A public-facing unicast address, equivalent to an IPv4 public address — globally unique and routable。
Link-local (fe80::/10)
Link-local only
Auto-configured, valid only within the same link (LAN segment) and not forwarded across routers。
Unique local (fc00::/7)
Private address
private address (ULA), equivalent to IPv4 private ranges such as 10.0.0.0/8, used for internal networks。
Multicast (ff00::/8)
One-to-many
Multicast address — IPv6 drops broadcast and uses multicast for one-to-many communication。
Loopback (::1/128)
Localhost
The local loopback address, equivalent to IPv4’s 127.0.0.1。
Unspecified (::/128)
No address
An all-zeros address means "No address yet", commonly used as a placeholder when no address is assigned.
Prefixes and subnetting
IPv6 no longer uses a dotted-decimal subnet mask, but instead usesPrefix lengthindicates the number of bits in the network portion. The standard practice is to assign sites /48，each subnet uses /64 (host portion is 64 bits, holding 2⁶⁴ addresses)。On /64 you simply carve out smaller prefixes as needed to create subnets. Unlike IPv4, IPv6 subnetting generally does not require fine-grained host counting to conserve addresses, so this tool uses"Split by number of subnets".
Key differences from IPv4
No broadcast address
IPv6 drops broadcast in favor of multicast (ff00::/8), so there is no"Broadcast address"Concept。
No dotted-decimal mask
There is only a prefix length (/64) — no dotted-decimal mask like 255.255.255.0。
No reserved network/broadcast address
/64 subnet — all of its 2⁶⁴ addresses are usable, with no need to subtract 2 as in IPv4.
Huge address space
128 bit addresses make the number of addresses per subnet astronomically large, so they are expressed as powers of 2。
Use cases and best practices
Network planning use cases
🏢 Enterprise IPv6 network planning
Carve a site /48 into per-department /64 subnets for hierarchical address planning and network isolation
🌐 Data center address design
Plan IPv6 network segments for racks and server clusters to optimize route aggregation and traffic management
☁️ Cloud network configuration
Plan IPv6 subnets in a cloud VPC and verify prefix ranges and address allocation
📱 Large-scale IoT deployment
Use IPv6’s vast address space to assign globally unique addresses to billions of IoT devices
🔒 Firewall and security policies
Identify address types and confirm prefix ranges to precisely configure IPv6 access control rules
🔧 Network troubleshooting
Compress/expand addresses and identify address classes to quickly pinpoint IPv6 configuration issues
Common prefix length reference table
/128 - Single address
1 address, used to identify a single host (such as the loopback ::1 or a router interface address）
/64 - Standard subnet
2⁶⁴ addresses — the most common IPv6 subnet granularity, required by Stateless Address Autoconfiguration (SLAAC)
/56 - Small site
256 /64 subnets — suitable for home broadband or small branch offices
/48 - Standard site
65536 /64 subnets — a typical prefix assigned by carriers to enterprise sites
IPv6 Planning best practices
🎯 Stick to the /64 subnet boundary
Use /64 uniformly for host subnets to ensure SLAAC, Neighbor Discovery, and similar mechanisms work correctly
📋 Hierarchical address planning
Carve prefixes hierarchically by geography, department, or purpose for easier route aggregation and documentation
🔍 Leverage address type semantics
Distinguish global unicast, unique local, and link-local addresses, and choose the right address class for your use case
🛡️ Reserve room for growth
IPv6 With addresses in abundance, reserve contiguous prefix blocks when planning to leave room for future growth