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.
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 "—").
Tips
- 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.
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.