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IP subnet calculator

Type an address with its prefix or mask to see the network, its usable range and masks. Split it into smaller subnets, or look up any prefix in the reference tables.

Network66.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
66.0.0.0
Broadcast address
67.255.255.255
First usable
66.0.0.1
Last usable
67.255.255.254
Usable hosts
33,554,430 (33,554,432 less the network and broadcast addresses)
Subnet mask
254.0.0.0
Wildcard mask
1.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/7
Type
Public public
Old class
A (default /8)
As numbers
Hex 42000000 · Integer 1107296256 to 1140850687
Reverse DNS zones
66.in-addr.arpa
67.in-addr.arpa
/7 is not on a 8-bit boundary, so it takes 2 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01000010.00000000.00000000.0000000066.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network01000010.00000000.00000000.0000000066.0.0.0
Broadcast01000011.11111111.11111111.1111111167.255.255.255
Split into smaller subnets/13
/8 (2)/9 (4)/10 (8)/11 (16)/12 (32)/13 (64)/14 (128)/15 (256)/16 (512)/17 (1,024)/18 (2,048)/19 (4,096)

66.0.0.0/7 makes 64 subnets of /13.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
166.0.0.0/1366.0.0.1 to 66.7.255.25466.7.255.255524,286
266.8.0.0/1366.8.0.1 to 66.15.255.25466.15.255.255524,286
366.16.0.0/1366.16.0.1 to 66.23.255.25466.23.255.255524,286
466.24.0.0/1366.24.0.1 to 66.31.255.25466.31.255.255524,286
566.32.0.0/1366.32.0.1 to 66.39.255.25466.39.255.255524,286
666.40.0.0/1366.40.0.1 to 66.47.255.25466.47.255.255524,286
766.48.0.0/1366.48.0.1 to 66.55.255.25466.55.255.255524,286
866.56.0.0/1366.56.0.1 to 66.63.255.25466.63.255.255524,286
966.64.0.0/1366.64.0.1 to 66.71.255.25466.71.255.255524,286
1066.72.0.0/1366.72.0.1 to 66.79.255.25466.79.255.255524,286
1166.80.0.0/1366.80.0.1 to 66.87.255.25466.87.255.255524,286
1266.88.0.0/1366.88.0.1 to 66.95.255.25466.95.255.255524,286
1366.96.0.0/1366.96.0.1 to 66.103.255.25466.103.255.255524,286
1466.104.0.0/1366.104.0.1 to 66.111.255.25466.111.255.255524,286
1566.112.0.0/1366.112.0.1 to 66.119.255.25466.119.255.255524,286
1666.120.0.0/1366.120.0.1 to 66.127.255.25466.127.255.255524,286
1766.128.0.0/1366.128.0.1 to 66.135.255.25466.135.255.255524,286
1866.136.0.0/1366.136.0.1 to 66.143.255.25466.143.255.255524,286
1966.144.0.0/1366.144.0.1 to 66.151.255.25466.151.255.255524,286
2066.152.0.0/1366.152.0.1 to 66.159.255.25466.159.255.255524,286
2166.160.0.0/1366.160.0.1 to 66.167.255.25466.167.255.255524,286
2266.168.0.0/1366.168.0.1 to 66.175.255.25466.175.255.255524,286
2366.176.0.0/1366.176.0.1 to 66.183.255.25466.183.255.255524,286
2466.184.0.0/1366.184.0.1 to 66.191.255.25466.191.255.255524,286
2566.192.0.0/1366.192.0.1 to 66.199.255.25466.199.255.255524,286
2666.200.0.0/1366.200.0.1 to 66.207.255.25466.207.255.255524,286
2766.208.0.0/1366.208.0.1 to 66.215.255.25466.215.255.255524,286
2866.216.0.0/1366.216.0.1 to 66.223.255.25466.223.255.255524,286
2966.224.0.0/1366.224.0.1 to 66.231.255.25466.231.255.255524,286
3066.232.0.0/1366.232.0.1 to 66.239.255.25466.239.255.255524,286
3166.240.0.0/1366.240.0.1 to 66.247.255.25466.247.255.255524,286
3266.248.0.0/1366.248.0.1 to 66.255.255.25466.255.255.255524,286
3367.0.0.0/1367.0.0.1 to 67.7.255.25467.7.255.255524,286
3467.8.0.0/1367.8.0.1 to 67.15.255.25467.15.255.255524,286
3567.16.0.0/1367.16.0.1 to 67.23.255.25467.23.255.255524,286
3667.24.0.0/1367.24.0.1 to 67.31.255.25467.31.255.255524,286
3767.32.0.0/1367.32.0.1 to 67.39.255.25467.39.255.255524,286
3867.40.0.0/1367.40.0.1 to 67.47.255.25467.47.255.255524,286
3967.48.0.0/1367.48.0.1 to 67.55.255.25467.55.255.255524,286
4067.56.0.0/1367.56.0.1 to 67.63.255.25467.63.255.255524,286
4167.64.0.0/1367.64.0.1 to 67.71.255.25467.71.255.255524,286
4267.72.0.0/1367.72.0.1 to 67.79.255.25467.79.255.255524,286
4367.80.0.0/1367.80.0.1 to 67.87.255.25467.87.255.255524,286
4467.88.0.0/1367.88.0.1 to 67.95.255.25467.95.255.255524,286
4567.96.0.0/1367.96.0.1 to 67.103.255.25467.103.255.255524,286
4667.104.0.0/1367.104.0.1 to 67.111.255.25467.111.255.255524,286
4767.112.0.0/1367.112.0.1 to 67.119.255.25467.119.255.255524,286
4867.120.0.0/1367.120.0.1 to 67.127.255.25467.127.255.255524,286
4967.128.0.0/1367.128.0.1 to 67.135.255.25467.135.255.255524,286
5067.136.0.0/1367.136.0.1 to 67.143.255.25467.143.255.255524,286
5167.144.0.0/1367.144.0.1 to 67.151.255.25467.151.255.255524,286
5267.152.0.0/1367.152.0.1 to 67.159.255.25467.159.255.255524,286
5367.160.0.0/1367.160.0.1 to 67.167.255.25467.167.255.255524,286
5467.168.0.0/1367.168.0.1 to 67.175.255.25467.175.255.255524,286
5567.176.0.0/1367.176.0.1 to 67.183.255.25467.183.255.255524,286
5667.184.0.0/1367.184.0.1 to 67.191.255.25467.191.255.255524,286
5767.192.0.0/1367.192.0.1 to 67.199.255.25467.199.255.255524,286
5867.200.0.0/1367.200.0.1 to 67.207.255.25467.207.255.255524,286
5967.208.0.0/1367.208.0.1 to 67.215.255.25467.215.255.255524,286
6067.216.0.0/1367.216.0.1 to 67.223.255.25467.223.255.255524,286
6167.224.0.0/1367.224.0.1 to 67.231.255.25467.231.255.255524,286
6267.232.0.0/1367.232.0.1 to 67.239.255.25467.239.255.255524,286
6367.240.0.0/1367.240.0.1 to 67.247.255.25467.247.255.255524,286
6467.248.0.0/1367.248.0.1 to 67.255.255.25467.255.255.255524,286

IPv4 CIDR reference (/0 to /32)

IPv4 prefix lengths
PrefixSubnet maskWildcardAddressesUsable hostsSizeTypical use
/00.0.0.0255.255.255.2554,294,967,2964,294,967,29416,777,216 × /24
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,6468,388,608 × /24
/2192.0.0.063.255.255.2551,073,741,8241,073,741,8224,194,304 × /24
/3224.0.0.031.255.255.255536,870,912536,870,9102,097,152 × /24
/4240.0.0.015.255.255.255268,435,456268,435,4541,048,576 × /24
/5248.0.0.07.255.255.255134,217,728134,217,726524,288 × /24
/6252.0.0.03.255.255.25567,108,86467,108,862262,144 × /24
/7254.0.0.01.255.255.25533,554,43233,554,430131,072 × /24
/8255.0.0.00.255.255.25516,777,21616,777,21465,536 × /24Old class A; 10.0.0.0/8
/9255.128.0.00.127.255.2558,388,6088,388,60632,768 × /24
/10255.192.0.00.63.255.2554,194,3044,194,30216,384 × /24
/11255.224.0.00.31.255.2552,097,1522,097,1508,192 × /24
/12255.240.0.00.15.255.2551,048,5761,048,5744,096 × /24172.16.0.0/12
/13255.248.0.00.7.255.255524,288524,2862,048 × /24
/14255.252.0.00.3.255.255262,144262,1421,024 × /24
/15255.254.0.00.1.255.255131,072131,070512 × /24
/16255.255.0.00.0.255.25565,53665,534256 × /24Old class B; 192.168.0.0/16
/17255.255.128.00.0.127.25532,76832,766128 × /24
/18255.255.192.00.0.63.25516,38416,38264 × /24
/19255.255.224.00.0.31.2558,1928,19032 × /24
/20255.255.240.00.0.15.2554,0964,09416 × /24
/21255.255.248.00.0.7.2552,0482,0468 × /24
/22255.255.252.00.0.3.2551,0241,0224 × /24Large office or guest Wi-Fi (1,022 hosts)
/23255.255.254.00.0.1.2555125102 × /24Larger office LAN (510 hosts)
/24255.255.255.00.0.0.2552562541 × /24Typical office LAN (old class C)
/25255.255.255.1280.0.0.1271281261/2 of a /24Smaller LAN or VLAN
/26255.255.255.1920.0.0.6364621/4 of a /24Smaller LAN or VLAN
/27255.255.255.2240.0.0.3132301/8 of a /24Small VLAN, phones, cameras
/28255.255.255.2400.0.0.1516141/16 of a /24Small VLAN, phones, cameras
/29255.255.255.2480.0.0.7861/32 of a /24Small fixed public block (5 usable)
/30255.255.255.2520.0.0.3421/64 of a /24Point-to-point (old style)
/31255.255.255.2540.0.0.1221/128 of a /24Point-to-point link (RFC 3021)
/32255.255.255.2550.0.0.0111/256 of a /24One host

IPv6 prefix reference

IPv6 prefix lengths
PrefixAddresses/64 LANs/48 sitesNibbleTypical use
/342,535,295,865,117,307,932,921,825,928,971,026,432 (2^125)2,305,843,009,213,693,95235,184,372,088,832NoAll global unicast (2000::/3)
/165,192,296,858,534,827,628,530,496,329,220,096 (2^112)281,474,976,710,6564,294,967,296Yes
/20324,518,553,658,426,726,783,156,020,576,256 (2^108)17,592,186,044,416268,435,456YesLarge provider allocation (RIPE minimum for some)
/29633,825,300,114,114,700,748,351,602,688 (2^99)34,359,738,368524,288NoRIPE allocation to a provider (often)
/3279,228,162,514,264,337,593,543,950,336 (2^96)4,294,967,29665,536YesProvider allocation (RIPE default)
/364,951,760,157,141,521,099,596,496,896 (2^92)268,435,4564,096Yes
/40309,485,009,821,345,068,724,781,056 (2^88)16,777,216256Yes
/4419,342,813,113,834,066,795,298,816 (2^84)1,048,57616Yes
/481,208,925,819,614,629,174,706,176 (2^80)65,5361YesOne site or organisation (RIPE PI / assignment)
/5275,557,863,725,914,323,419,136 (2^76)4,096Yes
/564,722,366,482,869,645,213,696 (2^72)256YesSmall site or home (common provider assignment)
/60295,147,905,179,352,825,856 (2^68)16YesSome home broadband (16 LANs)
/6418,446,744,073,709,551,616 (2^64)1YesOne LAN or VLAN (needed for SLAAC)
/7272,057,594,037,927,936 (2^56)1/256 of a /64Yes
/80281,474,976,710,656 (2^48)1/65,536 of a /64Yes
/964,294,967,2961/4,294,967,296 of a /64YesEmbeds an IPv4 address (NAT64)
/11265,5361/281,474,976,710,656 of a /64Yes
/1202561/72,057,594,037,927,936 of a /64Yes
/124161/1,152,921,504,606,846,976 of a /64Yes
/12641/4,611,686,018,427,387,904 of a /64No
/12721/9,223,372,036,854,775,808 of a /64NoPoint-to-point link (RFC 6164)
/12811/18,446,744,073,709,551,616 of a /64YesOne host or loopback

Private and special ranges

IPv4

Special-purpose ranges
RangeNameWhat it is
255.255.255.255/32Limited broadcastEvery host on the local network
0.0.0.0/8This networkNot routed; 0.0.0.0 means "any address" in settings
10.0.0.0/8Private (RFC 1918)Office and home networks; not routed on the internet
100.64.0.0/10Shared address space (CGNAT)Used by providers behind carrier-grade NAT (RFC 6598)
127.0.0.0/8LoopbackThis computer
169.254.0.0/16Link-local (APIPA)Self-assigned when no DHCP server answers
172.16.0.0/12Private (RFC 1918)Office and home networks; not routed on the internet
192.0.0.0/24IETF protocol assignmentsSpecial uses such as DS-Lite
192.0.2.0/24Documentation (TEST-NET-1)For examples; never used on a network
192.88.99.0/246to4 relay (deprecated)Formerly anycast for 6to4
192.168.0.0/16Private (RFC 1918)Office and home networks; not routed on the internet
198.18.0.0/15BenchmarkingNetwork equipment testing (RFC 2544)
198.51.100.0/24Documentation (TEST-NET-2)For examples; never used on a network
203.0.113.0/24Documentation (TEST-NET-3)For examples; never used on a network
224.0.0.0/4MulticastOne-to-many traffic, such as IPTV and routing protocols
240.0.0.0/4ReservedFuture use; not usable on most systems

IPv6

Special-purpose ranges
RangeNameWhat it is
::/128UnspecifiedNo address; :: means "any address" in settings
::1/128LoopbackThis computer
::ffff:0:0/96IPv4-mappedAn IPv4 address written as IPv6
64:ff9b::/96NAT64IPv4 addresses reached through a NAT64 gateway
100::/64Discard onlyTraffic sent here is dropped (RFC 6666)
2001:db8::/32DocumentationFor examples; never used on a network
2001::/32TeredoIPv6 tunnelled over IPv4 UDP
2002::/166to4IPv6 tunnelled over IPv4 (largely retired)
3fff::/20DocumentationFor examples (RFC 9637)
fc00::/7Unique local (ULA)Private IPv6, like RFC 1918; usually fd00::/8
fe80::/10Link-localEvery IPv6 interface has one; not routed
ff00::/8MulticastOne-to-many traffic; replaces broadcast
2000::/3Global unicastPublic internet addresses

About this tool

A network is written as an address and a prefix length, such as 192.168.1.0/24: the first 24 bits name the network and the rest number the devices on it. The calculator works out where the network starts and ends, how many devices it holds, its subnet and wildcard masks, and the reverse DNS zone to ask your provider for.

It also splits a network into equal smaller ones (one per VLAN or site), turns a range of addresses into the fewest CIDR blocks for a firewall rule, and lists every IPv4 prefix length and the common IPv6 ones in reference tables.

Common questions

Why are two addresses lost in every IPv4 subnet?

The first address names the network and the last is the broadcast address, so a /24 has 256 addresses but 254 for devices. A /31 (a link between two routers) and a /32 (one host) are the exceptions.

What size of IPv6 network should a LAN use?

Always /64. Devices pick their own address within it (SLAAC), which needs the full 64 bits. A site usually gets a /48 or /56 from its provider, which holds 65,536 or 256 LANs.

What is a wildcard mask?

The subnet mask turned inside out: 255.255.255.0 becomes 0.0.0.255. Cisco access lists and OSPF use it to say which bits must match.

Which ranges can I use inside an office?

IPv4: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. IPv6: unique local addresses from fd00::/8, though most networks use the public prefix from their provider.