How many addresses are in an IPv6 /13?

An IPv6 /13 contains 2¹¹⁵ addresses. The prefix fixes the first 13 bits; the remaining 115 bits identify individual addresses in the block.

How many /64 subnets fit in a /13?

A /13 can be divided into 2⁵¹ standard /64 LAN subnets. Each /64 holds 2⁶⁴ addresses, so the combined block is effectively inexhaustible for normal use.

How many /48 site allocations are in a /13?

A /13 contains 2³⁵ /48 site allocations. A /48 is the classic size assigned to a business site or campus.

What is the difference between /13 and /14?

A /13 is twice as large as /14. /13 has 2¹¹⁵ addresses; /14 has 2¹¹⁴. Each step down the prefix number doubles the address count.

How does /13 compare to /12?

A /12 is twice as large as /13. Moving from /13 to /12 adds one more fixed network bit, halving the host portion from 2¹¹⁵ to 2¹¹⁶ addresses.

How do I calculate an IPv6 /13 subnet?

Enter an IPv6 address and select prefix /13 in the calculator above — or paste full CIDR notation like 2001:db8::/13. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹¹⁵ addresses.

IPv6 /13 Subnet Calculator

Results update as you type

A /13 block fixes the first 13 bits of the address, leaving 115 host bits and 2¹¹⁵ total addresses. It subdivides into about 2⁵¹ /64 LAN subnets. That is also about 2³⁵ /48 site allocations. At the ISP tier, a /13 holds 2¹⁹ /32 ISP blocks. Prefixes in this range appear in BGP tables and RIR allocation policies as aggregation blocks above the standard ISP /32.

Prefix length

/128

/13 = 2¹¹⁵ addresses (≈ 4.15 × 10³⁴)

Results for 2000::/13

Documentation (RFC 3849)Global scope

Network / prefixThe first address — identifies the subnet itself

First addressSubnet-router anycast; first address in the block

Last addressThe highest address in this block

Prefix maskEquivalent to /13

Total addresses≈ 4.15 × 10³⁴ addresses

Address typeGlobally routable scope

More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown

Neighboring /13 subnets

Expanded address
Compressed address
Network (expanded)
Last address (expanded)
Prefix mask
Total addresses (exact)
Reverse DNS (PTR)
Host bits / network bits

Hextet breakdown

20010db8000000000000000000000000

NetworkSplit groupHost

Quick facts for IPv6 /13

Prefix mask: fff8::
Total addresses: 2¹¹⁵
Approx. count: 4.15 × 10³⁴
/64 subnets: 2⁵¹

IPv6 /13 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

mixhosthosthosthosthosthosthost

Network bits (13)Split hextetHost bits (115)

Network bits: 13
Host bits: 115
Prefix mask: fff8::
Total addresses: 2¹¹⁵
Approx. count: 4.15 × 10³⁴
/64 subnets: 2⁵¹
Addresses formula: 2^115
/64 relationship: 2⁵¹ × /64 subnets

Overview

Common use cases

Aggregating ISP /32 allocations in routing tables
Regional provider address planning
Large-scale subnetting study and documentation

Key facts

A /13 fixes 13 network bits and leaves 115 host bits — 2¹¹⁵ total addresses.
In network design terms, /13 is typically a RIR-level aggregation block.
You can subnet a /13 into about 2⁵¹ /64 LANs.
At site scale, /13 equals about 2³⁵ /48 allocations.
At ISP scale, /13 contains 2¹⁹ /32 blocks.

Design guidance

A /13 belongs in BGP aggregation and RIR allocation planning — not on a VLAN interface. If you are subnetting for a real deployment, work downward: carve /48 or /56 site blocks first, then assign one /64 per LAN. Announcing a single aggregated /13 (or larger) upstream keeps global routing tables manageable.

Practical example

An ISP holding 2001:db8::/13 might announce the entire /13 to upstream providers as one BGP route, then delegate /48 blocks such as 2001:db8:0001::/48 and 2001:db8:0002::/48 to business customers. Each customer subnets their /48 into /64 LANs.

Related RFCs and standards

RFC 4291IPv6 Addressing Architecture
RFC 3849IPv6 Documentation Address Prefix (2001:db8::/32)

Prefix sizing reference

Divide /13 into…

Prefix	Subnets	Addresses each
/14	2	2¹¹⁴
/15	4	2¹¹³
/17	16	2¹¹¹
/21	256	2¹⁰⁷

/13 fits inside…

Supernet	Addresses	/13s inside
/12	2¹¹⁶	2
/11	2¹¹⁷	4
/9	2¹¹⁹	16
/5	2¹²³	256

Notable /13 networks

2001:db8::/32Documentation prefix (RFC 3849)

Frequently asked questions

Common questions about IPv6 /13 blocks, prefix sizes, and use cases.

Common IPv6 prefix sizes

/3 /12 /16 /20 /24 /28 /32 /36 /40 /44 /48 /52 /56 /60 /64 /80 /96 /112 /120 /124 /126 /127 /128