IPv6 subnet cheat sheet (prefix chart)

This is the quick-reference IPv6 subnet cheat sheet: each common prefix length with how many /64 networks it holds, how many /56 home-size blocks fit inside it, the total number of addresses and what it is normally used for. To split a real prefix into its /64s, paste it into the FernTool IPv6 subnet calculator.

IPv6 prefix chart

Click any prefix to open it in the calculator. A smaller number after the slash means a bigger block: each step of 1 doubles the size, and each step of 4 (one hex digit) multiplies it by 16.

Prefix	/64 networks	/56 blocks	Addresses	Typical use
/16	281,474,976,710,656	1,099,511,627,776	2¹¹²	Very large allocations (rare)
/20	17,592,186,044,416	68,719,476,736	2¹⁰⁸	Large regional ISP allocation
/24	1,099,511,627,776	4,294,967,296	2¹⁰⁴	Big ISP or national network
/28	68,719,476,736	268,435,456	2¹⁰⁰
/29	34,359,738,368	134,217,728	2⁹⁹	Common registry allocation to a mid-size ISP
/32	4,294,967,296	16,777,216	2⁹⁶	Standard minimum allocation to an ISP (AFRINIC, RIPE, ARIN…)
/36	268,435,456	1,048,576	2⁹²	ISP region or large customer pool
/40	16,777,216	65,536	2⁸⁸	Large enterprise / ISP point of presence
/44	1,048,576	4,096	2⁸⁴	Big enterprise or campus
/48	65,536	256	2⁸⁰	A whole site or business (the classic end-site size)
/52	4,096	16	2⁷⁶	Medium site or branch office
/56	256	1	2⁷²	Typical home or small office from the ISP
/60	16	–	2⁶⁸	Small home delegation (some ISPs)
/64	1	–	18,446,744,073,709,551,616	One network: LAN, Wi-Fi, VLAN. Always use this for devices
/112	–	–	65,536	Sometimes used for small server links (65,536 addresses)
/120	–	–	256	Rare: 256 addresses, avoid for normal LANs
/126	–	–	4	Old-style point-to-point link (4 addresses)
/127	–	–	2	Router-to-router link (RFC 6164)
/128	–	–	1	One single address (loopback, a host route, a firewall rule)

The /64 column is the one that matters for planning: in IPv6 you count networks, not devices, because a single /64 already holds 18,446,744,073,709,551,616 addresses. Need to know which size to ask for? The calculator’s “How many networks do you need?” box answers it with one button, for example is a /56 enough for 20 networks?

The sizes you will actually meet

/32: what a registry such as AFRINIC gives an ISP. It holds 65,536 /48s.
/48: a business or site. 65,536 networks, enough for almost any company. Split a /48 into /56s.
/56: what most home fibre and business routers get from the ISP. 256 networks. List the /64s in a /56.
/60: a smaller home delegation from some ISPs. 16 networks.
/64: one network. Every LAN, Wi-Fi, guest network and VLAN should be exactly a /64.
/127 and /128: a router-to-router link and a single address.

Why every network should be a /64

Phones, laptops and smart devices choose their own address with SLAAC (stateless address autoconfiguration), which needs exactly 64 bits for the device part. Make a network smaller, say a /80 or /120, and many devices simply won’t get an address. So the rule is simple: /64 for anything with ordinary devices on it, /127 for links between two routers, /128 for a single address. Nothing in between for normal use.

Hex digits and nibble boundaries

An IPv6 address is 128 bits written as 8 groups of 4 hex digits. Each hex digit is 4 bits (a “nibble”), so prefixes on a multiple of 4 line up with whole digits and are easy to read:

/48: 2001:db8:abcd::/48: the first 3 groups are fixed
/52: 2001:db8:abcd:1000::/52: plus 1 more digit
/56: 2001:db8:abcd:1200::/56: 3½ groups fixed, your 256 networks are …:1200 to …:12ff
/60: 2001:db8:abcd:1230::/60: 16 networks, …:1230 to …:123f
/64: 2001:db8:abcd:1234::/64: 4 groups fixed, the last 4 groups are for devices

That is why ISPs and network teams hand out /48, /52, /56 and /60 rather than odd sizes like /57: you can see where one network ends just by reading the digits.

How to shorten an IPv6 address

Drop leading zeros in each group: 0db8 becomes db8, 0000 becomes 0.
Replace one run of all-zero groups with ::, the longest run, and only once per address.
Use lower-case letters (RFC 5952), so everyone writes the same address the same way.

Example: 2001:0db8:0000:0000:0000:ff00:0042:8329 shortens to 2001:db8::ff00:42:8329. Paste any address into the calculator’s one-click expand or shorten an IPv6 address box to get both forms, its /64 network and its reverse DNS name.

IPv6 address types (and their IPv4 equivalents)

Range	What it is	IPv4 equivalent
`::/128`	Unspecified address (“no address yet”)	0.0.0.0
`::1/128`	Loopback, your own machine	127.0.0.1
`2000::/3`	Global unicast: normal public internet addresses	Public IPv4
`fc00::/7 (fd00::/8 in use)`	Unique local: private, never on the internet	10.0.0.0/8, 192.168.0.0/16
`fe80::/10`	Link-local: every interface has one, never routed	169.254.0.0/16
`ff00::/8`	Multicast (there is no broadcast in IPv6)	224.0.0.0/4
`2001:db8::/32`	Documentation and examples only	192.0.2.0/24
`64:ff9b::/96`	NAT64: IPv4 addresses reached from IPv6-only networks	–
`::ffff:0:0/96`	IPv4-mapped addresses (::ffff:192.0.2.1)	–
`2002::/16`	6to4 tunnels (old, mostly retired)	–

Not sure if an address is public or private? The public vs private IP checker handles IPv6 too, and the IP lookup shows which network owns a public one.

How to work out any IPv6 prefix in your head

/64 networks in a prefix = 2 to the power of (64 − prefix). A /56 holds 2⁸ = 256; a /48 holds 2¹⁶ = 65,536.
One prefix inside another = 2 to the power of the difference. /56s in a /48: 2⁸ = 256. /60s in a /56: 2⁴ = 16.
Total addresses = 2 to the power of (128 − prefix). You will almost never need this number for IPv6.

IPv6 vs IPv4 cheat sheet

IPv4 uses 32-bit addresses and dotted masks like 255.255.255.0; you count usable hosts (size minus 2 for the network and broadcast address). IPv6 has no broadcast and no dotted mask, only the prefix length, and every address in the range is usable. For the IPv4 version of this table, with masks and wildcards, see the subnet mask cheat sheet or the subnet calculator. New to the slash notation? Read what CIDR notation means, and check whether your own connection has IPv6 with the IPv6 test.

Frequently asked questions

How many /64 subnets are in a /56?

A /56 holds 256 /64 subnets (2 to the power 8). That is enough for 256 separate networks such as LAN, Wi-Fi, guests and cameras.

How many /56 are in a /48?

A /48 holds 256 /56 blocks, or 65,536 /64 networks. ISPs often give a /48 to a business and a /56 to a home.

How many /48 are in a /32?

A /32 holds 65,536 /48s (2 to the power 16). A /32 is the usual minimum allocation a registry like AFRINIC or RIPE gives an ISP.

What is the smallest IPv6 subnet?

For a network with ordinary devices, the smallest you should use is a /64, because SLAAC needs 64 bits for the device part. For a link between two routers you can use a /127, and a single address is a /128.

What is the IPv6 equivalent of 192.168.x.x?

Unique local addresses in fd00::/8 (part of fc00::/7) play the same role as private IPv4 ranges like 192.168.0.0/16: they work inside your network but are never routed on the internet. Most homes simply use their public IPv6 prefix instead, with the router firewall blocking unwanted traffic.

What is a /64 in IPv6?

A /64 is one IPv6 network. The first 64 bits are the network prefix and the last 64 bits identify the device, giving 18,446,744,073,709,551,616 addresses. Every LAN or Wi-Fi network should be a /64.