How many addresses are in an IPv6 /19?

An IPv6 /19 contains 2¹⁰⁹ addresses. The prefix fixes the first 19 bits; the remaining 109 bits identify individual addresses in the block.

How many /64 subnets fit in a /19?

A /19 can be divided into 2⁴⁵ 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 /19?

A /19 contains 2²⁹ /48 site allocations. A /48 is the classic size assigned to a business site or campus.

What is the difference between /19 and /20?

A /19 is twice as large as /20. /19 has 2¹⁰⁹ addresses; /20 has 2¹⁰⁸. Each step down the prefix number doubles the address count.

How does /19 compare to /18?

A /18 is twice as large as /19. Moving from /19 to /18 adds one more fixed network bit, halving the host portion from 2¹⁰⁹ to 2¹¹⁰ addresses.

How do I calculate an IPv6 /19 subnet?

Enter an IPv6 address and select prefix /19 in the calculator above — or paste full CIDR notation like 2001:db8::/19. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹⁰⁹ addresses.

IPv6 /19 Subnet Calculator

Results update as you type

A /19 block fixes the first 19 bits of the address, leaving 109 host bits and 2¹⁰⁹ total addresses. It subdivides into about 2⁴⁵ /64 LAN subnets. That is also about 2²⁹ /48 site allocations. At the ISP tier, a /19 holds 2¹³ /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

/19 = 2¹⁰⁹ addresses (≈ 6.49 × 10³²)

Results for 2001::/19

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 /19

Total addresses≈ 6.49 × 10³² addresses

Address typeGlobally routable scope

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

Neighboring /19 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 /19

Prefix mask: ffff:e000::
Total addresses: 2¹⁰⁹
Approx. count: 6.49 × 10³²
/64 subnets: 2⁴⁵

IPv6 /19 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

netmixhosthosthosthosthosthost

Network bits (19)Split hextetHost bits (109)

Network bits: 19
Host bits: 109
Prefix mask: ffff:e000::
Total addresses: 2¹⁰⁹
Approx. count: 6.49 × 10³²
/64 subnets: 2⁴⁵
Addresses formula: 2^109
/64 relationship: 2⁴⁵ × /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 /19 fixes 19 network bits and leaves 109 host bits — 2¹⁰⁹ total addresses.
In network design terms, /19 is typically a RIR-level aggregation block.
You can subnet a /19 into about 2⁴⁵ /64 LANs.
At site scale, /19 equals about 2²⁹ /48 allocations.
At ISP scale, /19 contains 2¹³ /32 blocks.

Design guidance

A /19 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 /19 (or larger) upstream keeps global routing tables manageable.

Practical example

An ISP holding 2001:db8::/19 might announce the entire /19 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 /19 into…

Prefix	Subnets	Addresses each
/20	2	2¹⁰⁸
/21	4	2¹⁰⁷
/23	16	2¹⁰⁵
/27	256	2¹⁰¹

/19 fits inside…

Supernet	Addresses	/19s inside
/18	2¹¹⁰	2
/17	2¹¹¹	4
/15	2¹¹³	16
/11	2¹¹⁷	256

Notable /19 networks

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

Frequently asked questions

Common questions about IPv6 /19 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