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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.

Network66.243.0.0/16
Usable hosts65,534
Subnet mask255.255.0.0
Addresses65,536
Network address
66.243.0.0
Broadcast address
66.243.255.255
First usable
66.243.0.1
Last usable
66.243.255.254
Usable hosts
65,534 (65,536 less the network and broadcast addresses)
Subnet mask
255.255.0.0
Wildcard mask
0.0.255.255 (Cisco ACLs, OSPF)
Prefix length
/16
Type
Public public
Old class
A (default /8)
As numbers
Hex 42F30000 · Integer 1123221504 to 1123287039
Reverse DNS zone
243.66.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01000010.11110011..00000000.0000000066.243.0.0
Subnet mask11111111.11111111..00000000.00000000255.255.0.0
Network01000010.11110011..00000000.0000000066.243.0.0
Broadcast01000010.11110011..11111111.1111111166.243.255.255
Split into smaller subnets/23
/17 (2)/18 (4)/19 (8)/20 (16)/21 (32)/22 (64)/23 (128)/24 (256)/25 (512)/26 (1,024)/27 (2,048)/28 (4,096)

66.243.0.0/16 makes 128 subnets of /23.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
166.243.0.0/2366.243.0.1 to 66.243.1.25466.243.1.255510
266.243.2.0/2366.243.2.1 to 66.243.3.25466.243.3.255510
366.243.4.0/2366.243.4.1 to 66.243.5.25466.243.5.255510
466.243.6.0/2366.243.6.1 to 66.243.7.25466.243.7.255510
566.243.8.0/2366.243.8.1 to 66.243.9.25466.243.9.255510
666.243.10.0/2366.243.10.1 to 66.243.11.25466.243.11.255510
766.243.12.0/2366.243.12.1 to 66.243.13.25466.243.13.255510
866.243.14.0/2366.243.14.1 to 66.243.15.25466.243.15.255510
966.243.16.0/2366.243.16.1 to 66.243.17.25466.243.17.255510
1066.243.18.0/2366.243.18.1 to 66.243.19.25466.243.19.255510
1166.243.20.0/2366.243.20.1 to 66.243.21.25466.243.21.255510
1266.243.22.0/2366.243.22.1 to 66.243.23.25466.243.23.255510
1366.243.24.0/2366.243.24.1 to 66.243.25.25466.243.25.255510
1466.243.26.0/2366.243.26.1 to 66.243.27.25466.243.27.255510
1566.243.28.0/2366.243.28.1 to 66.243.29.25466.243.29.255510
1666.243.30.0/2366.243.30.1 to 66.243.31.25466.243.31.255510
1766.243.32.0/2366.243.32.1 to 66.243.33.25466.243.33.255510
1866.243.34.0/2366.243.34.1 to 66.243.35.25466.243.35.255510
1966.243.36.0/2366.243.36.1 to 66.243.37.25466.243.37.255510
2066.243.38.0/2366.243.38.1 to 66.243.39.25466.243.39.255510
2166.243.40.0/2366.243.40.1 to 66.243.41.25466.243.41.255510
2266.243.42.0/2366.243.42.1 to 66.243.43.25466.243.43.255510
2366.243.44.0/2366.243.44.1 to 66.243.45.25466.243.45.255510
2466.243.46.0/2366.243.46.1 to 66.243.47.25466.243.47.255510
2566.243.48.0/2366.243.48.1 to 66.243.49.25466.243.49.255510
2666.243.50.0/2366.243.50.1 to 66.243.51.25466.243.51.255510
2766.243.52.0/2366.243.52.1 to 66.243.53.25466.243.53.255510
2866.243.54.0/2366.243.54.1 to 66.243.55.25466.243.55.255510
2966.243.56.0/2366.243.56.1 to 66.243.57.25466.243.57.255510
3066.243.58.0/2366.243.58.1 to 66.243.59.25466.243.59.255510
3166.243.60.0/2366.243.60.1 to 66.243.61.25466.243.61.255510
3266.243.62.0/2366.243.62.1 to 66.243.63.25466.243.63.255510
3366.243.64.0/2366.243.64.1 to 66.243.65.25466.243.65.255510
3466.243.66.0/2366.243.66.1 to 66.243.67.25466.243.67.255510
3566.243.68.0/2366.243.68.1 to 66.243.69.25466.243.69.255510
3666.243.70.0/2366.243.70.1 to 66.243.71.25466.243.71.255510
3766.243.72.0/2366.243.72.1 to 66.243.73.25466.243.73.255510
3866.243.74.0/2366.243.74.1 to 66.243.75.25466.243.75.255510
3966.243.76.0/2366.243.76.1 to 66.243.77.25466.243.77.255510
4066.243.78.0/2366.243.78.1 to 66.243.79.25466.243.79.255510
4166.243.80.0/2366.243.80.1 to 66.243.81.25466.243.81.255510
4266.243.82.0/2366.243.82.1 to 66.243.83.25466.243.83.255510
4366.243.84.0/2366.243.84.1 to 66.243.85.25466.243.85.255510
4466.243.86.0/2366.243.86.1 to 66.243.87.25466.243.87.255510
4566.243.88.0/2366.243.88.1 to 66.243.89.25466.243.89.255510
4666.243.90.0/2366.243.90.1 to 66.243.91.25466.243.91.255510
4766.243.92.0/2366.243.92.1 to 66.243.93.25466.243.93.255510
4866.243.94.0/2366.243.94.1 to 66.243.95.25466.243.95.255510
4966.243.96.0/2366.243.96.1 to 66.243.97.25466.243.97.255510
5066.243.98.0/2366.243.98.1 to 66.243.99.25466.243.99.255510
5166.243.100.0/2366.243.100.1 to 66.243.101.25466.243.101.255510
5266.243.102.0/2366.243.102.1 to 66.243.103.25466.243.103.255510
5366.243.104.0/2366.243.104.1 to 66.243.105.25466.243.105.255510
5466.243.106.0/2366.243.106.1 to 66.243.107.25466.243.107.255510
5566.243.108.0/2366.243.108.1 to 66.243.109.25466.243.109.255510
5666.243.110.0/2366.243.110.1 to 66.243.111.25466.243.111.255510
5766.243.112.0/2366.243.112.1 to 66.243.113.25466.243.113.255510
5866.243.114.0/2366.243.114.1 to 66.243.115.25466.243.115.255510
5966.243.116.0/2366.243.116.1 to 66.243.117.25466.243.117.255510
6066.243.118.0/2366.243.118.1 to 66.243.119.25466.243.119.255510
6166.243.120.0/2366.243.120.1 to 66.243.121.25466.243.121.255510
6266.243.122.0/2366.243.122.1 to 66.243.123.25466.243.123.255510
6366.243.124.0/2366.243.124.1 to 66.243.125.25466.243.125.255510
6466.243.126.0/2366.243.126.1 to 66.243.127.25466.243.127.255510
6566.243.128.0/2366.243.128.1 to 66.243.129.25466.243.129.255510
6666.243.130.0/2366.243.130.1 to 66.243.131.25466.243.131.255510
6766.243.132.0/2366.243.132.1 to 66.243.133.25466.243.133.255510
6866.243.134.0/2366.243.134.1 to 66.243.135.25466.243.135.255510
6966.243.136.0/2366.243.136.1 to 66.243.137.25466.243.137.255510
7066.243.138.0/2366.243.138.1 to 66.243.139.25466.243.139.255510
7166.243.140.0/2366.243.140.1 to 66.243.141.25466.243.141.255510
7266.243.142.0/2366.243.142.1 to 66.243.143.25466.243.143.255510
7366.243.144.0/2366.243.144.1 to 66.243.145.25466.243.145.255510
7466.243.146.0/2366.243.146.1 to 66.243.147.25466.243.147.255510
7566.243.148.0/2366.243.148.1 to 66.243.149.25466.243.149.255510
7666.243.150.0/2366.243.150.1 to 66.243.151.25466.243.151.255510
7766.243.152.0/2366.243.152.1 to 66.243.153.25466.243.153.255510
7866.243.154.0/2366.243.154.1 to 66.243.155.25466.243.155.255510
7966.243.156.0/2366.243.156.1 to 66.243.157.25466.243.157.255510
8066.243.158.0/2366.243.158.1 to 66.243.159.25466.243.159.255510
8166.243.160.0/2366.243.160.1 to 66.243.161.25466.243.161.255510
8266.243.162.0/2366.243.162.1 to 66.243.163.25466.243.163.255510
8366.243.164.0/2366.243.164.1 to 66.243.165.25466.243.165.255510
8466.243.166.0/2366.243.166.1 to 66.243.167.25466.243.167.255510
8566.243.168.0/2366.243.168.1 to 66.243.169.25466.243.169.255510
8666.243.170.0/2366.243.170.1 to 66.243.171.25466.243.171.255510
8766.243.172.0/2366.243.172.1 to 66.243.173.25466.243.173.255510
8866.243.174.0/2366.243.174.1 to 66.243.175.25466.243.175.255510
8966.243.176.0/2366.243.176.1 to 66.243.177.25466.243.177.255510
9066.243.178.0/2366.243.178.1 to 66.243.179.25466.243.179.255510
9166.243.180.0/2366.243.180.1 to 66.243.181.25466.243.181.255510
9266.243.182.0/2366.243.182.1 to 66.243.183.25466.243.183.255510
9366.243.184.0/2366.243.184.1 to 66.243.185.25466.243.185.255510
9466.243.186.0/2366.243.186.1 to 66.243.187.25466.243.187.255510
9566.243.188.0/2366.243.188.1 to 66.243.189.25466.243.189.255510
9666.243.190.0/2366.243.190.1 to 66.243.191.25466.243.191.255510
9766.243.192.0/2366.243.192.1 to 66.243.193.25466.243.193.255510
9866.243.194.0/2366.243.194.1 to 66.243.195.25466.243.195.255510
9966.243.196.0/2366.243.196.1 to 66.243.197.25466.243.197.255510
10066.243.198.0/2366.243.198.1 to 66.243.199.25466.243.199.255510
10166.243.200.0/2366.243.200.1 to 66.243.201.25466.243.201.255510
10266.243.202.0/2366.243.202.1 to 66.243.203.25466.243.203.255510
10366.243.204.0/2366.243.204.1 to 66.243.205.25466.243.205.255510
10466.243.206.0/2366.243.206.1 to 66.243.207.25466.243.207.255510
10566.243.208.0/2366.243.208.1 to 66.243.209.25466.243.209.255510
10666.243.210.0/2366.243.210.1 to 66.243.211.25466.243.211.255510
10766.243.212.0/2366.243.212.1 to 66.243.213.25466.243.213.255510
10866.243.214.0/2366.243.214.1 to 66.243.215.25466.243.215.255510
10966.243.216.0/2366.243.216.1 to 66.243.217.25466.243.217.255510
11066.243.218.0/2366.243.218.1 to 66.243.219.25466.243.219.255510
11166.243.220.0/2366.243.220.1 to 66.243.221.25466.243.221.255510
11266.243.222.0/2366.243.222.1 to 66.243.223.25466.243.223.255510
11366.243.224.0/2366.243.224.1 to 66.243.225.25466.243.225.255510
11466.243.226.0/2366.243.226.1 to 66.243.227.25466.243.227.255510
11566.243.228.0/2366.243.228.1 to 66.243.229.25466.243.229.255510
11666.243.230.0/2366.243.230.1 to 66.243.231.25466.243.231.255510
11766.243.232.0/2366.243.232.1 to 66.243.233.25466.243.233.255510
11866.243.234.0/2366.243.234.1 to 66.243.235.25466.243.235.255510
11966.243.236.0/2366.243.236.1 to 66.243.237.25466.243.237.255510
12066.243.238.0/2366.243.238.1 to 66.243.239.25466.243.239.255510
12166.243.240.0/2366.243.240.1 to 66.243.241.25466.243.241.255510
12266.243.242.0/2366.243.242.1 to 66.243.243.25466.243.243.255510
12366.243.244.0/2366.243.244.1 to 66.243.245.25466.243.245.255510
12466.243.246.0/2366.243.246.1 to 66.243.247.25466.243.247.255510
12566.243.248.0/2366.243.248.1 to 66.243.249.25466.243.249.255510
12666.243.250.0/2366.243.250.1 to 66.243.251.25466.243.251.255510
12766.243.252.0/2366.243.252.1 to 66.243.253.25466.243.253.255510
12866.243.254.0/2366.243.254.1 to 66.243.255.25466.243.255.255510

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.