IPv6 CIDR Reference Table — Address Counts by Prefix Length (Free)

A reference table showing the number of addresses and equivalent /64 subnets for every IPv6 prefix length from /0 to /128. Enter how many /64 subnets you need and the best-fitting prefix length is highlighted automatically.

Last updated: 2026-09-11

IPv6 CIDR reference table (/0 to /128)

The host bit count, total address count, and equivalent /64 subnet count for every prefix length.

Prefix	Host bits	Total addresses	/64 subnets	Typical use
/0	128	340,282,366,920,938,463,463,374,607,431,768,211,456	18,446,744,073,709,551,616	The entire address space (theoretical value; never actually allocated)
/1	127	170,141,183,460,469,231,731,687,303,715,884,105,728	9,223,372,036,854,775,808
/2	126	85,070,591,730,234,615,865,843,651,857,942,052,864	4,611,686,018,427,387,904
/3	125	42,535,295,865,117,307,932,921,825,928,971,026,432	2,305,843,009,213,693,952	The entire global unicast address range (2000::/3)
/4	124	21,267,647,932,558,653,966,460,912,964,485,513,216	1,152,921,504,606,846,976
/5	123	10,633,823,966,279,326,983,230,456,482,242,756,608	576,460,752,303,423,488
/6	122	5,316,911,983,139,663,491,615,228,241,121,378,304	288,230,376,151,711,744
/7	121	2,658,455,991,569,831,745,807,614,120,560,689,152	144,115,188,075,855,872	The entire unique local address range (fc00::/7 — the IPv6 equivalent of IPv4 private addresses)
/8	120	1,329,227,995,784,915,872,903,807,060,280,344,576	72,057,594,037,927,936
/9	119	664,613,997,892,457,936,451,903,530,140,172,288	36,028,797,018,963,968
/10	118	332,306,998,946,228,968,225,951,765,070,086,144	18,014,398,509,481,984	The entire link-local address range (fe80::/10)
/11	117	166,153,499,473,114,484,112,975,882,535,043,072	9,007,199,254,740,992
/12	116	83,076,749,736,557,242,056,487,941,267,521,536	4,503,599,627,370,496
/13	115	41,538,374,868,278,621,028,243,970,633,760,768	2,251,799,813,685,248
/14	114	20,769,187,434,139,310,514,121,985,316,880,384	1,125,899,906,842,624
/15	113	10,384,593,717,069,655,257,060,992,658,440,192	562,949,953,421,312
/16	112	5,192,296,858,534,827,628,530,496,329,220,096	281,474,976,710,656
/17	111	2,596,148,429,267,413,814,265,248,164,610,048	140,737,488,355,328
/18	110	1,298,074,214,633,706,907,132,624,082,305,024	70,368,744,177,664
/19	109	649,037,107,316,853,453,566,312,041,152,512	35,184,372,088,832
/20	108	324,518,553,658,426,726,783,156,020,576,256	17,592,186,044,416
/21	107	162,259,276,829,213,363,391,578,010,288,128	8,796,093,022,208
/22	106	81,129,638,414,606,681,695,789,005,144,064	4,398,046,511,104
/23	105	40,564,819,207,303,340,847,894,502,572,032	2,199,023,255,552
/24	104	20,282,409,603,651,670,423,947,251,286,016	1,099,511,627,776
/25	103	10,141,204,801,825,835,211,973,625,643,008	549,755,813,888
/26	102	5,070,602,400,912,917,605,986,812,821,504	274,877,906,944
/27	101	2,535,301,200,456,458,802,993,406,410,752	137,438,953,472
/28	100	1,267,650,600,228,229,401,496,703,205,376	68,719,476,736
/29	99	633,825,300,114,114,700,748,351,602,688	34,359,738,368
/30	98	316,912,650,057,057,350,374,175,801,344	17,179,869,184
/31	97	158,456,325,028,528,675,187,087,900,672	8,589,934,592
/32	96	79,228,162,514,264,337,593,543,950,336	4,294,967,296	A common minimum allocation size RIRs give to large ISPs and carriers
/33	95	39,614,081,257,132,168,796,771,975,168	2,147,483,648
/34	94	19,807,040,628,566,084,398,385,987,584	1,073,741,824
/35	93	9,903,520,314,283,042,199,192,993,792	536,870,912
/36	92	4,951,760,157,141,521,099,596,496,896	268,435,456
/37	91	2,475,880,078,570,760,549,798,248,448	134,217,728
/38	90	1,237,940,039,285,380,274,899,124,224	67,108,864
/39	89	618,970,019,642,690,137,449,562,112	33,554,432
/40	88	309,485,009,821,345,068,724,781,056	16,777,216
/41	87	154,742,504,910,672,534,362,390,528	8,388,608
/42	86	77,371,252,455,336,267,181,195,264	4,194,304
/43	85	38,685,626,227,668,133,590,597,632	2,097,152
/44	84	19,342,813,113,834,066,795,298,816	1,048,576
/45	83	9,671,406,556,917,033,397,649,408	524,288
/46	82	4,835,703,278,458,516,698,824,704	262,144
/47	81	2,417,851,639,229,258,349,412,352	131,072
/48	80	1,208,925,819,614,629,174,706,176	65,536	The standard allocation for an organization (the common guideline of "one /48 per organization")
/49	79	604,462,909,807,314,587,353,088	32,768
/50	78	302,231,454,903,657,293,676,544	16,384
/51	77	151,115,727,451,828,646,838,272	8,192
/52	76	75,557,863,725,914,323,419,136	4,096
/53	75	37,778,931,862,957,161,709,568	2,048
/54	74	18,889,465,931,478,580,854,784	1,024
/55	73	9,444,732,965,739,290,427,392	512
/56	72	4,722,366,482,869,645,213,696	256	A size ISPs often assign to homes and small offices
/57	71	2,361,183,241,434,822,606,848	128
/58	70	1,180,591,620,717,411,303,424	64
/59	69	590,295,810,358,705,651,712	32
/60	68	295,147,905,179,352,825,856	16	A typical allocation for a small site
/61	67	147,573,952,589,676,412,928	8
/62	66	73,786,976,294,838,206,464	4
/63	65	36,893,488,147,419,103,232	2
/64	64	18,446,744,073,709,551,616	1	The standard single subnet size (the minimum unit required for SLAAC/EUI-64 address autoconfiguration)
/65	63	9,223,372,036,854,775,808	—
/66	62	4,611,686,018,427,387,904	—
/67	61	2,305,843,009,213,693,952	—
/68	60	1,152,921,504,606,846,976	—
/69	59	576,460,752,303,423,488	—
/70	58	288,230,376,151,711,744	—
/71	57	144,115,188,075,855,872	—
/72	56	72,057,594,037,927,936	—
/73	55	36,028,797,018,963,968	—
/74	54	18,014,398,509,481,984	—
/75	53	9,007,199,254,740,992	—
/76	52	4,503,599,627,370,496	—
/77	51	2,251,799,813,685,248	—
/78	50	1,125,899,906,842,624	—
/79	49	562,949,953,421,312	—
/80	48	281,474,976,710,656	—
/81	47	140,737,488,355,328	—
/82	46	70,368,744,177,664	—
/83	45	35,184,372,088,832	—
/84	44	17,592,186,044,416	—
/85	43	8,796,093,022,208	—
/86	42	4,398,046,511,104	—
/87	41	2,199,023,255,552	—
/88	40	1,099,511,627,776	—
/89	39	549,755,813,888	—
/90	38	274,877,906,944	—
/91	37	137,438,953,472	—
/92	36	68,719,476,736	—
/93	35	34,359,738,368	—
/94	34	17,179,869,184	—
/95	33	8,589,934,592	—
/96	32	4,294,967,296	—
/97	31	2,147,483,648	—
/98	30	1,073,741,824	—
/99	29	536,870,912	—
/100	28	268,435,456	—
/101	27	134,217,728	—
/102	26	67,108,864	—
/103	25	33,554,432	—
/104	24	16,777,216	—
/105	23	8,388,608	—
/106	22	4,194,304	—
/107	21	2,097,152	—
/108	20	1,048,576	—
/109	19	524,288	—
/110	18	262,144	—
/111	17	131,072	—
/112	16	65,536	—
/113	15	32,768	—
/114	14	16,384	—
/115	13	8,192	—
/116	12	4,096	—
/117	11	2,048	—
/118	10	1,024	—
/119	9	512	—
/120	8	256	—
/121	7	128	—
/122	6	64	—
/123	5	32	—
/124	4	16	—
/125	3	8	—
/126	2	4	—
/127	1	2	—	Reserved for point-to-point links only (RFC 6164 — just the 2 addresses between two routers)
/128	0	1	—	A single host address (such as a loopback)

The /64 subnet count shows how many standard-sized (/64) subnets fit inside that block (blocks with a prefix of 65 or longer are smaller than a /64, shown as "—").

What Is the IPv6 Address Space and CIDR Notation (Prefix Length)?

IPv6 uses a 128-bit address space, which is an astronomically larger range than IPv4's 32 bits — specifically 2 to the 96th power times bigger. CIDR (Classless Inter-Domain Routing) notation is what divides this vast space into a network portion and a host portion, expressing the number of network bits as a number after a slash, as in "2001:db8::/32" (the prefix length). Unlike IPv4, there's no separate convention for writing out a subnet mask (such as 255.255.255.0) — the prefix length alone uniquely determines the size of the block.

IPv6's design never really anticipated fine-grained allocations with a prefix length of 65 or higher, and /64 has become the de facto standard size for a single subnet. That's because SLAAC (Stateless Address Autoconfiguration) relies on a mechanism called EUI-64 to generate a 64-bit interface identifier from a device's MAC address and similar inputs, and the practice of assigning a full /64 to every LAN segment is now firmly established across the industry. This tool lists, for every prefix length from /0 through /128, the total number of addresses contained in that block along with its equivalent count of /64 subnets, and it can also work backward from a target number of subnets to determine the best-fitting prefix length.

How to Use the IPv6 CIDR Reference Table

Estimate the number of /64 subnets you need Think through how many /64 subnets your upcoming network design will require — based on the number of sites, departments, or VLANs involved.
Enter that number in the box at the top Type your estimated subnet count into the "Find by required number of /64 subnets" field, and the smallest prefix length that can accommodate it is determined automatically.
Check the resulting prefix length A message such as "You need a block of /{prefix} or larger" appears. You can use this as a reference figure when requesting an allocation from an ISP or cloud provider.
Compare neighboring prefix lengths in the table The matching row is highlighted directly in the table. It's worth also comparing the row one step larger and one step smaller to see how much the address count changes, so your design leaves comfortable room for future growth.

Tips for getting more out of it

IPv6 subnet planning is usually framed around "how many /64 subnets do I need" rather than host counts — SLAAC (Stateless Address Autoconfiguration) requires each LAN segment to be assigned a full /64.
Residential ISPs commonly assign a /56 or /60, while business allocations are typically a /48. It's worth checking your ISP's allocation policy before signing up.
/127 is a special prefix length formally approved by RFC 6164 (2015) exclusively for point-to-point router links — the IPv6 equivalent of IPv4's /31.
Enter the number of /64 subnets you need in the box above, and the smallest prefix length that fits will be automatically determined and highlighted in the table below.

When the IPv6 CIDR Reference Table Comes in Handy

Designing IPv6 addressing for an internal corporate network

Add up the /64 subnets needed at each headquarters, branch office, and site to figure out what overall prefix length (such as /48 or /56) your organization should secure.

Verifying the block your ISP has assigned

When your ISP notifies you of a /56 or /48 prefix, you can instantly check exactly how many /64 subnets that block actually contains.

Planning IPv6 subnets inside a cloud VPC

When a cloud provider hands you an IPv6 CIDR block, this table helps you decide what prefix length to use when carving out subnets per region or availability zone.

Producing supporting figures for network diagrams and proposals

When you need to state exactly how many subnets a given prefix length provides in a network diagram or a client proposal, you can cite the table's values directly rather than calculating them by hand.

Sanity-checking a subnetting plan before a migration

Before migrating a dual-stack network fully to IPv6, use the table to confirm that the prefix length you're planning to request will comfortably cover both your current subnet count and a reasonable growth margin.

Glossary

CIDR (Classless Inter-Domain Routing): A notation for splitting an IP address into a network portion and a host portion using an arbitrary bit count (the prefix length) instead of the old fixed address classes. In IPv6, this notation alone expresses the size of a block.
Prefix length: The number that follows the slash in CIDR notation, indicating how many bits starting from the beginning of the address are used as the network portion. A smaller number represents a wider address range, and a larger number a narrower one.
/64 subnet: The de facto standard size for a single subnet in IPv6. It's the minimum unit required for SLAAC-based automatic address generation to work correctly, and LAN segments are normally assigned exactly this size.
IPv6 address space: The full addressable range of IPv6, expressed in 128 bits. It's vastly larger than IPv4's 32-bit space by many orders of magnitude, which underlies IPv6's design philosophy of allocating generously rather than conserving every bit.
Host bit count: The prefix length subtracted from 128, giving the number of bits available for the host portion at the end of the address. Two raised to this number equals the total number of addresses contained in that block.
SLAAC (Stateless Address Autoconfiguration): A mechanism that lets a device generate its own IPv6 address automatically from information advertised by a router combined with its MAC address, without relying on a management server such as DHCP. It's designed around the assumption of a /64 subnet.
RIR (Regional Internet Registry): An organization that manages IP address allocation on a regional basis. RIRs set the policies for handing out prefix lengths such as /32 or /48 to ISPs and large organizations.
Dual stack: A network configuration in which IPv4 and IPv6 run side by side on the same device or link. Many organizations plan their /64 subnet layout for IPv6 while still operating IPv4 in parallel during the transition period.

FAQ

Technically the concept still exists, but in practice it's never used — everything is expressed as a prefix length (like /64) instead. Since IPv6 isn't designed around NAT, there's no need to fine-tune a mask just to save addresses.

Because SLAAC (Stateless Address Autoconfiguration) assumes a 64-bit interface identifier (EUI-64), typically derived from a device's MAC address, fills the host portion. Assigning a prefix longer than /64 to an individual LAN segment can break this autoconfiguration.

IPv4 typically relies on NAT to translate private addresses into a shared global address, but IPv6 is designed to give every device a globally routable address directly, so it doesn't assume NAT. IPv4 also tends to be allocated in small increments (like /24 or /29) to conserve a scarce resource, while IPv6 is handed out in much larger, round blocks like /48 or /56.

Start by checking the prefix length your ISP or data center gave you. If it's a /48 or /56, you can split it into multiple /64 subnets — use this tool to enter how many /64 subnets you'll need and confirm your design leaves enough room to grow.

Side Note — Why IPv6 Doesn't Use "Subnet Masks"

IPv4 separates the network and host portions using a subnet mask (a value like 255.255.255.0), but IPv6 is expressed almost exclusively through CIDR-style prefix lengths (like /64), and splitting the mask at an arbitrary bit position is rarely done in practice. This reflects IPv6's underlying design philosophy: address space is abundant, so there's no need to conserve it down to the last bit.

In practice, a fixed 64-bit host portion has become the de facto standard for IPv6. That's because SLAAC (Stateless Address Autoconfiguration) relies on a mechanism called EUI-64 to derive a 64-bit interface identifier from a device's MAC address; assigning a subnet shorter than /64 to an individual LAN segment breaks this autoconfiguration mechanism.

In the IPv4 era, "don't waste a single address" was the guiding principle, but IPv6 flips that around — the recommendation now is to allocate generously for future growth. Even RFC guidance suggests handing residential connections a /56 or /48, sizes that would have been unthinkably large under IPv4's rules. That shift in mindset is one of the biggest differences between the two protocols.

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