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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.

Network81.16.0.0/13
Usable hosts524,286
Subnet mask255.248.0.0
Addresses524,288
Network address
81.16.0.0
Broadcast address
81.23.255.255
First usable
81.16.0.1
Last usable
81.23.255.254
Usable hosts
524,286 (524,288 less the network and broadcast addresses)
Subnet mask
255.248.0.0
Wildcard mask
0.7.255.255 (Cisco ACLs, OSPF)
Prefix length
/13
Type
Public public
Old class
A (default /8)
As numbers
Hex 51100000 · Integer 1360003072 to 1360527359
Reverse DNS zones
16.81.in-addr.arpa
17.81.in-addr.arpa
18.81.in-addr.arpa
19.81.in-addr.arpa
20.81.in-addr.arpa
21.81.in-addr.arpa
22.81.in-addr.arpa
23.81.in-addr.arpa
/13 is not on a 8-bit boundary, so it takes 8 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01010001.00010000.00000000.0000000081.16.0.0
Subnet mask11111111.11111000.00000000.00000000255.248.0.0
Network01010001.00010000.00000000.0000000081.16.0.0
Broadcast01010001.00010111.11111111.1111111181.23.255.255
Split into smaller subnets/20
/14 (2)/15 (4)/16 (8)/17 (16)/18 (32)/19 (64)/20 (128)/21 (256)/22 (512)/23 (1,024)/24 (2,048)/25 (4,096)

81.16.0.0/13 makes 128 subnets of /20.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
181.16.0.0/2081.16.0.1 to 81.16.15.25481.16.15.2554,094
281.16.16.0/2081.16.16.1 to 81.16.31.25481.16.31.2554,094
381.16.32.0/2081.16.32.1 to 81.16.47.25481.16.47.2554,094
481.16.48.0/2081.16.48.1 to 81.16.63.25481.16.63.2554,094
581.16.64.0/2081.16.64.1 to 81.16.79.25481.16.79.2554,094
681.16.80.0/2081.16.80.1 to 81.16.95.25481.16.95.2554,094
781.16.96.0/2081.16.96.1 to 81.16.111.25481.16.111.2554,094
881.16.112.0/2081.16.112.1 to 81.16.127.25481.16.127.2554,094
981.16.128.0/2081.16.128.1 to 81.16.143.25481.16.143.2554,094
1081.16.144.0/2081.16.144.1 to 81.16.159.25481.16.159.2554,094
1181.16.160.0/2081.16.160.1 to 81.16.175.25481.16.175.2554,094
1281.16.176.0/2081.16.176.1 to 81.16.191.25481.16.191.2554,094
1381.16.192.0/2081.16.192.1 to 81.16.207.25481.16.207.2554,094
1481.16.208.0/2081.16.208.1 to 81.16.223.25481.16.223.2554,094
1581.16.224.0/2081.16.224.1 to 81.16.239.25481.16.239.2554,094
1681.16.240.0/2081.16.240.1 to 81.16.255.25481.16.255.2554,094
1781.17.0.0/2081.17.0.1 to 81.17.15.25481.17.15.2554,094
1881.17.16.0/2081.17.16.1 to 81.17.31.25481.17.31.2554,094
1981.17.32.0/2081.17.32.1 to 81.17.47.25481.17.47.2554,094
2081.17.48.0/2081.17.48.1 to 81.17.63.25481.17.63.2554,094
2181.17.64.0/2081.17.64.1 to 81.17.79.25481.17.79.2554,094
2281.17.80.0/2081.17.80.1 to 81.17.95.25481.17.95.2554,094
2381.17.96.0/2081.17.96.1 to 81.17.111.25481.17.111.2554,094
2481.17.112.0/2081.17.112.1 to 81.17.127.25481.17.127.2554,094
2581.17.128.0/2081.17.128.1 to 81.17.143.25481.17.143.2554,094
2681.17.144.0/2081.17.144.1 to 81.17.159.25481.17.159.2554,094
2781.17.160.0/2081.17.160.1 to 81.17.175.25481.17.175.2554,094
2881.17.176.0/2081.17.176.1 to 81.17.191.25481.17.191.2554,094
2981.17.192.0/2081.17.192.1 to 81.17.207.25481.17.207.2554,094
3081.17.208.0/2081.17.208.1 to 81.17.223.25481.17.223.2554,094
3181.17.224.0/2081.17.224.1 to 81.17.239.25481.17.239.2554,094
3281.17.240.0/2081.17.240.1 to 81.17.255.25481.17.255.2554,094
3381.18.0.0/2081.18.0.1 to 81.18.15.25481.18.15.2554,094
3481.18.16.0/2081.18.16.1 to 81.18.31.25481.18.31.2554,094
3581.18.32.0/2081.18.32.1 to 81.18.47.25481.18.47.2554,094
3681.18.48.0/2081.18.48.1 to 81.18.63.25481.18.63.2554,094
3781.18.64.0/2081.18.64.1 to 81.18.79.25481.18.79.2554,094
3881.18.80.0/2081.18.80.1 to 81.18.95.25481.18.95.2554,094
3981.18.96.0/2081.18.96.1 to 81.18.111.25481.18.111.2554,094
4081.18.112.0/2081.18.112.1 to 81.18.127.25481.18.127.2554,094
4181.18.128.0/2081.18.128.1 to 81.18.143.25481.18.143.2554,094
4281.18.144.0/2081.18.144.1 to 81.18.159.25481.18.159.2554,094
4381.18.160.0/2081.18.160.1 to 81.18.175.25481.18.175.2554,094
4481.18.176.0/2081.18.176.1 to 81.18.191.25481.18.191.2554,094
4581.18.192.0/2081.18.192.1 to 81.18.207.25481.18.207.2554,094
4681.18.208.0/2081.18.208.1 to 81.18.223.25481.18.223.2554,094
4781.18.224.0/2081.18.224.1 to 81.18.239.25481.18.239.2554,094
4881.18.240.0/2081.18.240.1 to 81.18.255.25481.18.255.2554,094
4981.19.0.0/2081.19.0.1 to 81.19.15.25481.19.15.2554,094
5081.19.16.0/2081.19.16.1 to 81.19.31.25481.19.31.2554,094
5181.19.32.0/2081.19.32.1 to 81.19.47.25481.19.47.2554,094
5281.19.48.0/2081.19.48.1 to 81.19.63.25481.19.63.2554,094
5381.19.64.0/2081.19.64.1 to 81.19.79.25481.19.79.2554,094
5481.19.80.0/2081.19.80.1 to 81.19.95.25481.19.95.2554,094
5581.19.96.0/2081.19.96.1 to 81.19.111.25481.19.111.2554,094
5681.19.112.0/2081.19.112.1 to 81.19.127.25481.19.127.2554,094
5781.19.128.0/2081.19.128.1 to 81.19.143.25481.19.143.2554,094
5881.19.144.0/2081.19.144.1 to 81.19.159.25481.19.159.2554,094
5981.19.160.0/2081.19.160.1 to 81.19.175.25481.19.175.2554,094
6081.19.176.0/2081.19.176.1 to 81.19.191.25481.19.191.2554,094
6181.19.192.0/2081.19.192.1 to 81.19.207.25481.19.207.2554,094
6281.19.208.0/2081.19.208.1 to 81.19.223.25481.19.223.2554,094
6381.19.224.0/2081.19.224.1 to 81.19.239.25481.19.239.2554,094
6481.19.240.0/2081.19.240.1 to 81.19.255.25481.19.255.2554,094
6581.20.0.0/2081.20.0.1 to 81.20.15.25481.20.15.2554,094
6681.20.16.0/2081.20.16.1 to 81.20.31.25481.20.31.2554,094
6781.20.32.0/2081.20.32.1 to 81.20.47.25481.20.47.2554,094
6881.20.48.0/2081.20.48.1 to 81.20.63.25481.20.63.2554,094
6981.20.64.0/2081.20.64.1 to 81.20.79.25481.20.79.2554,094
7081.20.80.0/2081.20.80.1 to 81.20.95.25481.20.95.2554,094
7181.20.96.0/2081.20.96.1 to 81.20.111.25481.20.111.2554,094
7281.20.112.0/2081.20.112.1 to 81.20.127.25481.20.127.2554,094
7381.20.128.0/2081.20.128.1 to 81.20.143.25481.20.143.2554,094
7481.20.144.0/2081.20.144.1 to 81.20.159.25481.20.159.2554,094
7581.20.160.0/2081.20.160.1 to 81.20.175.25481.20.175.2554,094
7681.20.176.0/2081.20.176.1 to 81.20.191.25481.20.191.2554,094
7781.20.192.0/2081.20.192.1 to 81.20.207.25481.20.207.2554,094
7881.20.208.0/2081.20.208.1 to 81.20.223.25481.20.223.2554,094
7981.20.224.0/2081.20.224.1 to 81.20.239.25481.20.239.2554,094
8081.20.240.0/2081.20.240.1 to 81.20.255.25481.20.255.2554,094
8181.21.0.0/2081.21.0.1 to 81.21.15.25481.21.15.2554,094
8281.21.16.0/2081.21.16.1 to 81.21.31.25481.21.31.2554,094
8381.21.32.0/2081.21.32.1 to 81.21.47.25481.21.47.2554,094
8481.21.48.0/2081.21.48.1 to 81.21.63.25481.21.63.2554,094
8581.21.64.0/2081.21.64.1 to 81.21.79.25481.21.79.2554,094
8681.21.80.0/2081.21.80.1 to 81.21.95.25481.21.95.2554,094
8781.21.96.0/2081.21.96.1 to 81.21.111.25481.21.111.2554,094
8881.21.112.0/2081.21.112.1 to 81.21.127.25481.21.127.2554,094
8981.21.128.0/2081.21.128.1 to 81.21.143.25481.21.143.2554,094
9081.21.144.0/2081.21.144.1 to 81.21.159.25481.21.159.2554,094
9181.21.160.0/2081.21.160.1 to 81.21.175.25481.21.175.2554,094
9281.21.176.0/2081.21.176.1 to 81.21.191.25481.21.191.2554,094
9381.21.192.0/2081.21.192.1 to 81.21.207.25481.21.207.2554,094
9481.21.208.0/2081.21.208.1 to 81.21.223.25481.21.223.2554,094
9581.21.224.0/2081.21.224.1 to 81.21.239.25481.21.239.2554,094
9681.21.240.0/2081.21.240.1 to 81.21.255.25481.21.255.2554,094
9781.22.0.0/2081.22.0.1 to 81.22.15.25481.22.15.2554,094
9881.22.16.0/2081.22.16.1 to 81.22.31.25481.22.31.2554,094
9981.22.32.0/2081.22.32.1 to 81.22.47.25481.22.47.2554,094
10081.22.48.0/2081.22.48.1 to 81.22.63.25481.22.63.2554,094
10181.22.64.0/2081.22.64.1 to 81.22.79.25481.22.79.2554,094
10281.22.80.0/2081.22.80.1 to 81.22.95.25481.22.95.2554,094
10381.22.96.0/2081.22.96.1 to 81.22.111.25481.22.111.2554,094
10481.22.112.0/2081.22.112.1 to 81.22.127.25481.22.127.2554,094
10581.22.128.0/2081.22.128.1 to 81.22.143.25481.22.143.2554,094
10681.22.144.0/2081.22.144.1 to 81.22.159.25481.22.159.2554,094
10781.22.160.0/2081.22.160.1 to 81.22.175.25481.22.175.2554,094
10881.22.176.0/2081.22.176.1 to 81.22.191.25481.22.191.2554,094
10981.22.192.0/2081.22.192.1 to 81.22.207.25481.22.207.2554,094
11081.22.208.0/2081.22.208.1 to 81.22.223.25481.22.223.2554,094
11181.22.224.0/2081.22.224.1 to 81.22.239.25481.22.239.2554,094
11281.22.240.0/2081.22.240.1 to 81.22.255.25481.22.255.2554,094
11381.23.0.0/2081.23.0.1 to 81.23.15.25481.23.15.2554,094
11481.23.16.0/2081.23.16.1 to 81.23.31.25481.23.31.2554,094
11581.23.32.0/2081.23.32.1 to 81.23.47.25481.23.47.2554,094
11681.23.48.0/2081.23.48.1 to 81.23.63.25481.23.63.2554,094
11781.23.64.0/2081.23.64.1 to 81.23.79.25481.23.79.2554,094
11881.23.80.0/2081.23.80.1 to 81.23.95.25481.23.95.2554,094
11981.23.96.0/2081.23.96.1 to 81.23.111.25481.23.111.2554,094
12081.23.112.0/2081.23.112.1 to 81.23.127.25481.23.127.2554,094
12181.23.128.0/2081.23.128.1 to 81.23.143.25481.23.143.2554,094
12281.23.144.0/2081.23.144.1 to 81.23.159.25481.23.159.2554,094
12381.23.160.0/2081.23.160.1 to 81.23.175.25481.23.175.2554,094
12481.23.176.0/2081.23.176.1 to 81.23.191.25481.23.191.2554,094
12581.23.192.0/2081.23.192.1 to 81.23.207.25481.23.207.2554,094
12681.23.208.0/2081.23.208.1 to 81.23.223.25481.23.223.2554,094
12781.23.224.0/2081.23.224.1 to 81.23.239.25481.23.239.2554,094
12881.23.240.0/2081.23.240.1 to 81.23.255.25481.23.255.2554,094

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.