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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.

Network20.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
20.0.0.0
Broadcast address
21.255.255.255
First usable
20.0.0.1
Last usable
21.255.255.254
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 14000000 · Integer 335544320 to 369098751
Reverse DNS zones
20.in-addr.arpa
21.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
Address00010100.00000000.00000000.0000000020.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network00010100.00000000.00000000.0000000020.0.0.0
Broadcast00010101.11111111.11111111.1111111121.255.255.255
Split into smaller subnets/14
/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)

20.0.0.0/7 makes 128 subnets of /14.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
120.0.0.0/1420.0.0.1 to 20.3.255.25420.3.255.255262,142
220.4.0.0/1420.4.0.1 to 20.7.255.25420.7.255.255262,142
320.8.0.0/1420.8.0.1 to 20.11.255.25420.11.255.255262,142
420.12.0.0/1420.12.0.1 to 20.15.255.25420.15.255.255262,142
520.16.0.0/1420.16.0.1 to 20.19.255.25420.19.255.255262,142
620.20.0.0/1420.20.0.1 to 20.23.255.25420.23.255.255262,142
720.24.0.0/1420.24.0.1 to 20.27.255.25420.27.255.255262,142
820.28.0.0/1420.28.0.1 to 20.31.255.25420.31.255.255262,142
920.32.0.0/1420.32.0.1 to 20.35.255.25420.35.255.255262,142
1020.36.0.0/1420.36.0.1 to 20.39.255.25420.39.255.255262,142
1120.40.0.0/1420.40.0.1 to 20.43.255.25420.43.255.255262,142
1220.44.0.0/1420.44.0.1 to 20.47.255.25420.47.255.255262,142
1320.48.0.0/1420.48.0.1 to 20.51.255.25420.51.255.255262,142
1420.52.0.0/1420.52.0.1 to 20.55.255.25420.55.255.255262,142
1520.56.0.0/1420.56.0.1 to 20.59.255.25420.59.255.255262,142
1620.60.0.0/1420.60.0.1 to 20.63.255.25420.63.255.255262,142
1720.64.0.0/1420.64.0.1 to 20.67.255.25420.67.255.255262,142
1820.68.0.0/1420.68.0.1 to 20.71.255.25420.71.255.255262,142
1920.72.0.0/1420.72.0.1 to 20.75.255.25420.75.255.255262,142
2020.76.0.0/1420.76.0.1 to 20.79.255.25420.79.255.255262,142
2120.80.0.0/1420.80.0.1 to 20.83.255.25420.83.255.255262,142
2220.84.0.0/1420.84.0.1 to 20.87.255.25420.87.255.255262,142
2320.88.0.0/1420.88.0.1 to 20.91.255.25420.91.255.255262,142
2420.92.0.0/1420.92.0.1 to 20.95.255.25420.95.255.255262,142
2520.96.0.0/1420.96.0.1 to 20.99.255.25420.99.255.255262,142
2620.100.0.0/1420.100.0.1 to 20.103.255.25420.103.255.255262,142
2720.104.0.0/1420.104.0.1 to 20.107.255.25420.107.255.255262,142
2820.108.0.0/1420.108.0.1 to 20.111.255.25420.111.255.255262,142
2920.112.0.0/1420.112.0.1 to 20.115.255.25420.115.255.255262,142
3020.116.0.0/1420.116.0.1 to 20.119.255.25420.119.255.255262,142
3120.120.0.0/1420.120.0.1 to 20.123.255.25420.123.255.255262,142
3220.124.0.0/1420.124.0.1 to 20.127.255.25420.127.255.255262,142
3320.128.0.0/1420.128.0.1 to 20.131.255.25420.131.255.255262,142
3420.132.0.0/1420.132.0.1 to 20.135.255.25420.135.255.255262,142
3520.136.0.0/1420.136.0.1 to 20.139.255.25420.139.255.255262,142
3620.140.0.0/1420.140.0.1 to 20.143.255.25420.143.255.255262,142
3720.144.0.0/1420.144.0.1 to 20.147.255.25420.147.255.255262,142
3820.148.0.0/1420.148.0.1 to 20.151.255.25420.151.255.255262,142
3920.152.0.0/1420.152.0.1 to 20.155.255.25420.155.255.255262,142
4020.156.0.0/1420.156.0.1 to 20.159.255.25420.159.255.255262,142
4120.160.0.0/1420.160.0.1 to 20.163.255.25420.163.255.255262,142
4220.164.0.0/1420.164.0.1 to 20.167.255.25420.167.255.255262,142
4320.168.0.0/1420.168.0.1 to 20.171.255.25420.171.255.255262,142
4420.172.0.0/1420.172.0.1 to 20.175.255.25420.175.255.255262,142
4520.176.0.0/1420.176.0.1 to 20.179.255.25420.179.255.255262,142
4620.180.0.0/1420.180.0.1 to 20.183.255.25420.183.255.255262,142
4720.184.0.0/1420.184.0.1 to 20.187.255.25420.187.255.255262,142
4820.188.0.0/1420.188.0.1 to 20.191.255.25420.191.255.255262,142
4920.192.0.0/1420.192.0.1 to 20.195.255.25420.195.255.255262,142
5020.196.0.0/1420.196.0.1 to 20.199.255.25420.199.255.255262,142
5120.200.0.0/1420.200.0.1 to 20.203.255.25420.203.255.255262,142
5220.204.0.0/1420.204.0.1 to 20.207.255.25420.207.255.255262,142
5320.208.0.0/1420.208.0.1 to 20.211.255.25420.211.255.255262,142
5420.212.0.0/1420.212.0.1 to 20.215.255.25420.215.255.255262,142
5520.216.0.0/1420.216.0.1 to 20.219.255.25420.219.255.255262,142
5620.220.0.0/1420.220.0.1 to 20.223.255.25420.223.255.255262,142
5720.224.0.0/1420.224.0.1 to 20.227.255.25420.227.255.255262,142
5820.228.0.0/1420.228.0.1 to 20.231.255.25420.231.255.255262,142
5920.232.0.0/1420.232.0.1 to 20.235.255.25420.235.255.255262,142
6020.236.0.0/1420.236.0.1 to 20.239.255.25420.239.255.255262,142
6120.240.0.0/1420.240.0.1 to 20.243.255.25420.243.255.255262,142
6220.244.0.0/1420.244.0.1 to 20.247.255.25420.247.255.255262,142
6320.248.0.0/1420.248.0.1 to 20.251.255.25420.251.255.255262,142
6420.252.0.0/1420.252.0.1 to 20.255.255.25420.255.255.255262,142
6521.0.0.0/1421.0.0.1 to 21.3.255.25421.3.255.255262,142
6621.4.0.0/1421.4.0.1 to 21.7.255.25421.7.255.255262,142
6721.8.0.0/1421.8.0.1 to 21.11.255.25421.11.255.255262,142
6821.12.0.0/1421.12.0.1 to 21.15.255.25421.15.255.255262,142
6921.16.0.0/1421.16.0.1 to 21.19.255.25421.19.255.255262,142
7021.20.0.0/1421.20.0.1 to 21.23.255.25421.23.255.255262,142
7121.24.0.0/1421.24.0.1 to 21.27.255.25421.27.255.255262,142
7221.28.0.0/1421.28.0.1 to 21.31.255.25421.31.255.255262,142
7321.32.0.0/1421.32.0.1 to 21.35.255.25421.35.255.255262,142
7421.36.0.0/1421.36.0.1 to 21.39.255.25421.39.255.255262,142
7521.40.0.0/1421.40.0.1 to 21.43.255.25421.43.255.255262,142
7621.44.0.0/1421.44.0.1 to 21.47.255.25421.47.255.255262,142
7721.48.0.0/1421.48.0.1 to 21.51.255.25421.51.255.255262,142
7821.52.0.0/1421.52.0.1 to 21.55.255.25421.55.255.255262,142
7921.56.0.0/1421.56.0.1 to 21.59.255.25421.59.255.255262,142
8021.60.0.0/1421.60.0.1 to 21.63.255.25421.63.255.255262,142
8121.64.0.0/1421.64.0.1 to 21.67.255.25421.67.255.255262,142
8221.68.0.0/1421.68.0.1 to 21.71.255.25421.71.255.255262,142
8321.72.0.0/1421.72.0.1 to 21.75.255.25421.75.255.255262,142
8421.76.0.0/1421.76.0.1 to 21.79.255.25421.79.255.255262,142
8521.80.0.0/1421.80.0.1 to 21.83.255.25421.83.255.255262,142
8621.84.0.0/1421.84.0.1 to 21.87.255.25421.87.255.255262,142
8721.88.0.0/1421.88.0.1 to 21.91.255.25421.91.255.255262,142
8821.92.0.0/1421.92.0.1 to 21.95.255.25421.95.255.255262,142
8921.96.0.0/1421.96.0.1 to 21.99.255.25421.99.255.255262,142
9021.100.0.0/1421.100.0.1 to 21.103.255.25421.103.255.255262,142
9121.104.0.0/1421.104.0.1 to 21.107.255.25421.107.255.255262,142
9221.108.0.0/1421.108.0.1 to 21.111.255.25421.111.255.255262,142
9321.112.0.0/1421.112.0.1 to 21.115.255.25421.115.255.255262,142
9421.116.0.0/1421.116.0.1 to 21.119.255.25421.119.255.255262,142
9521.120.0.0/1421.120.0.1 to 21.123.255.25421.123.255.255262,142
9621.124.0.0/1421.124.0.1 to 21.127.255.25421.127.255.255262,142
9721.128.0.0/1421.128.0.1 to 21.131.255.25421.131.255.255262,142
9821.132.0.0/1421.132.0.1 to 21.135.255.25421.135.255.255262,142
9921.136.0.0/1421.136.0.1 to 21.139.255.25421.139.255.255262,142
10021.140.0.0/1421.140.0.1 to 21.143.255.25421.143.255.255262,142
10121.144.0.0/1421.144.0.1 to 21.147.255.25421.147.255.255262,142
10221.148.0.0/1421.148.0.1 to 21.151.255.25421.151.255.255262,142
10321.152.0.0/1421.152.0.1 to 21.155.255.25421.155.255.255262,142
10421.156.0.0/1421.156.0.1 to 21.159.255.25421.159.255.255262,142
10521.160.0.0/1421.160.0.1 to 21.163.255.25421.163.255.255262,142
10621.164.0.0/1421.164.0.1 to 21.167.255.25421.167.255.255262,142
10721.168.0.0/1421.168.0.1 to 21.171.255.25421.171.255.255262,142
10821.172.0.0/1421.172.0.1 to 21.175.255.25421.175.255.255262,142
10921.176.0.0/1421.176.0.1 to 21.179.255.25421.179.255.255262,142
11021.180.0.0/1421.180.0.1 to 21.183.255.25421.183.255.255262,142
11121.184.0.0/1421.184.0.1 to 21.187.255.25421.187.255.255262,142
11221.188.0.0/1421.188.0.1 to 21.191.255.25421.191.255.255262,142
11321.192.0.0/1421.192.0.1 to 21.195.255.25421.195.255.255262,142
11421.196.0.0/1421.196.0.1 to 21.199.255.25421.199.255.255262,142
11521.200.0.0/1421.200.0.1 to 21.203.255.25421.203.255.255262,142
11621.204.0.0/1421.204.0.1 to 21.207.255.25421.207.255.255262,142
11721.208.0.0/1421.208.0.1 to 21.211.255.25421.211.255.255262,142
11821.212.0.0/1421.212.0.1 to 21.215.255.25421.215.255.255262,142
11921.216.0.0/1421.216.0.1 to 21.219.255.25421.219.255.255262,142
12021.220.0.0/1421.220.0.1 to 21.223.255.25421.223.255.255262,142
12121.224.0.0/1421.224.0.1 to 21.227.255.25421.227.255.255262,142
12221.228.0.0/1421.228.0.1 to 21.231.255.25421.231.255.255262,142
12321.232.0.0/1421.232.0.1 to 21.235.255.25421.235.255.255262,142
12421.236.0.0/1421.236.0.1 to 21.239.255.25421.239.255.255262,142
12521.240.0.0/1421.240.0.1 to 21.243.255.25421.243.255.255262,142
12621.244.0.0/1421.244.0.1 to 21.247.255.25421.247.255.255262,142
12721.248.0.0/1421.248.0.1 to 21.251.255.25421.251.255.255262,142
12821.252.0.0/1421.252.0.1 to 21.255.255.25421.255.255.255262,142

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.