How many addresses are in an IPv6 /15?

An IPv6 /15 contains 2¹¹³ addresses. The prefix fixes the first 15 bits; the remaining 113 bits identify individual addresses in the block.

How many /64 subnets fit in a /15?

A /15 can be divided into 2⁴⁹ 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 /15?

A /15 contains 2³³ /48 site allocations. A /48 is the classic size assigned to a business site or campus.

What is the difference between /15 and /16?

A /15 is twice as large as /16. /15 has 2¹¹³ addresses; /16 has 2¹¹². Each step down the prefix number doubles the address count.

How does /15 compare to /14?

A /14 is twice as large as /15. Moving from /15 to /14 adds one more fixed network bit, halving the host portion from 2¹¹³ to 2¹¹⁴ addresses.

How do I calculate an IPv6 /15 subnet?

Enter an IPv6 address and select prefix /15 in the calculator above — or paste full CIDR notation like 2001:db8::/15. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹¹³ addresses.

IPv6 /15 Subnet Calculator

Results update as you type

A /15 block fixes the first 15 bits of the address, leaving 113 host bits and 2¹¹³ total addresses. It subdivides into about 2⁴⁹ /64 LAN subnets. That is also about 2³³ /48 site allocations. At the ISP tier, a /15 holds 2¹⁷ /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

/15 = 2¹¹³ addresses (≈ 1.04 × 10³⁴)

Results for 2000::/15

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 /15

Total addresses≈ 1.04 × 10³⁴ addresses

Address typeGlobally routable scope

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

Neighboring /15 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 /15

Prefix mask: fffe::
Total addresses: 2¹¹³
Approx. count: 1.04 × 10³⁴
/64 subnets: 2⁴⁹

IPv6 /15 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

mixhosthosthosthosthosthosthost

Network bits (15)Split hextetHost bits (113)

Network bits: 15
Host bits: 113
Prefix mask: fffe::
Total addresses: 2¹¹³
Approx. count: 1.04 × 10³⁴
/64 subnets: 2⁴⁹
Addresses formula: 2^113
/64 relationship: 2⁴⁹ × /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 /15 fixes 15 network bits and leaves 113 host bits — 2¹¹³ total addresses.
In network design terms, /15 is typically a RIR-level aggregation block.
You can subnet a /15 into about 2⁴⁹ /64 LANs.
At site scale, /15 equals about 2³³ /48 allocations.
At ISP scale, /15 contains 2¹⁷ /32 blocks.

Design guidance

A /15 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 /15 (or larger) upstream keeps global routing tables manageable.

Practical example

An ISP holding 2001:db8::/15 might announce the entire /15 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 /15 into…

Prefix	Subnets	Addresses each
/16	2	2¹¹²
/17	4	2¹¹¹
/19	16	2¹⁰⁹
/23	256	2¹⁰⁵

/15 fits inside…

Supernet	Addresses	/15s inside
/14	2¹¹⁴	2
/13	2¹¹⁵	4
/11	2¹¹⁷	16
/7	2¹²¹	256

Notable /15 networks

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

Frequently asked questions

Common questions about IPv6 /15 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