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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.

Network51.128.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
51.128.0.0
Broadcast address
51.191.255.255
First usable
51.128.0.1
Last usable
51.191.255.254
Usable hosts
4,194,302 (4,194,304 less the network and broadcast addresses)
Subnet mask
255.192.0.0
Wildcard mask
0.63.255.255 (Cisco ACLs, OSPF)
Prefix length
/10
Type
Public public
Old class
A (default /8)
As numbers
Hex 33800000 · Integer 864026624 to 868220927
Reverse DNS zones
128.51.in-addr.arpa
129.51.in-addr.arpa
130.51.in-addr.arpa
131.51.in-addr.arpa
132.51.in-addr.arpa
133.51.in-addr.arpa
134.51.in-addr.arpa
135.51.in-addr.arpa
136.51.in-addr.arpa
137.51.in-addr.arpa
138.51.in-addr.arpa
139.51.in-addr.arpa
140.51.in-addr.arpa
141.51.in-addr.arpa
142.51.in-addr.arpa
143.51.in-addr.arpa
and 48 more
/10 is not on a 8-bit boundary, so it takes 64 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00110011.10000000.00000000.0000000051.128.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network00110011.10000000.00000000.0000000051.128.0.0
Broadcast00110011.10111111.11111111.1111111151.191.255.255
Split into smaller subnets/17
/11 (2)/12 (4)/13 (8)/14 (16)/15 (32)/16 (64)/17 (128)/18 (256)/19 (512)/20 (1,024)/21 (2,048)/22 (4,096)

51.128.0.0/10 makes 128 subnets of /17.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
151.128.0.0/1751.128.0.1 to 51.128.127.25451.128.127.25532,766
251.128.128.0/1751.128.128.1 to 51.128.255.25451.128.255.25532,766
351.129.0.0/1751.129.0.1 to 51.129.127.25451.129.127.25532,766
451.129.128.0/1751.129.128.1 to 51.129.255.25451.129.255.25532,766
551.130.0.0/1751.130.0.1 to 51.130.127.25451.130.127.25532,766
651.130.128.0/1751.130.128.1 to 51.130.255.25451.130.255.25532,766
751.131.0.0/1751.131.0.1 to 51.131.127.25451.131.127.25532,766
851.131.128.0/1751.131.128.1 to 51.131.255.25451.131.255.25532,766
951.132.0.0/1751.132.0.1 to 51.132.127.25451.132.127.25532,766
1051.132.128.0/1751.132.128.1 to 51.132.255.25451.132.255.25532,766
1151.133.0.0/1751.133.0.1 to 51.133.127.25451.133.127.25532,766
1251.133.128.0/1751.133.128.1 to 51.133.255.25451.133.255.25532,766
1351.134.0.0/1751.134.0.1 to 51.134.127.25451.134.127.25532,766
1451.134.128.0/1751.134.128.1 to 51.134.255.25451.134.255.25532,766
1551.135.0.0/1751.135.0.1 to 51.135.127.25451.135.127.25532,766
1651.135.128.0/1751.135.128.1 to 51.135.255.25451.135.255.25532,766
1751.136.0.0/1751.136.0.1 to 51.136.127.25451.136.127.25532,766
1851.136.128.0/1751.136.128.1 to 51.136.255.25451.136.255.25532,766
1951.137.0.0/1751.137.0.1 to 51.137.127.25451.137.127.25532,766
2051.137.128.0/1751.137.128.1 to 51.137.255.25451.137.255.25532,766
2151.138.0.0/1751.138.0.1 to 51.138.127.25451.138.127.25532,766
2251.138.128.0/1751.138.128.1 to 51.138.255.25451.138.255.25532,766
2351.139.0.0/1751.139.0.1 to 51.139.127.25451.139.127.25532,766
2451.139.128.0/1751.139.128.1 to 51.139.255.25451.139.255.25532,766
2551.140.0.0/1751.140.0.1 to 51.140.127.25451.140.127.25532,766
2651.140.128.0/1751.140.128.1 to 51.140.255.25451.140.255.25532,766
2751.141.0.0/1751.141.0.1 to 51.141.127.25451.141.127.25532,766
2851.141.128.0/1751.141.128.1 to 51.141.255.25451.141.255.25532,766
2951.142.0.0/1751.142.0.1 to 51.142.127.25451.142.127.25532,766
3051.142.128.0/1751.142.128.1 to 51.142.255.25451.142.255.25532,766
3151.143.0.0/1751.143.0.1 to 51.143.127.25451.143.127.25532,766
3251.143.128.0/1751.143.128.1 to 51.143.255.25451.143.255.25532,766
3351.144.0.0/1751.144.0.1 to 51.144.127.25451.144.127.25532,766
3451.144.128.0/1751.144.128.1 to 51.144.255.25451.144.255.25532,766
3551.145.0.0/1751.145.0.1 to 51.145.127.25451.145.127.25532,766
3651.145.128.0/1751.145.128.1 to 51.145.255.25451.145.255.25532,766
3751.146.0.0/1751.146.0.1 to 51.146.127.25451.146.127.25532,766
3851.146.128.0/1751.146.128.1 to 51.146.255.25451.146.255.25532,766
3951.147.0.0/1751.147.0.1 to 51.147.127.25451.147.127.25532,766
4051.147.128.0/1751.147.128.1 to 51.147.255.25451.147.255.25532,766
4151.148.0.0/1751.148.0.1 to 51.148.127.25451.148.127.25532,766
4251.148.128.0/1751.148.128.1 to 51.148.255.25451.148.255.25532,766
4351.149.0.0/1751.149.0.1 to 51.149.127.25451.149.127.25532,766
4451.149.128.0/1751.149.128.1 to 51.149.255.25451.149.255.25532,766
4551.150.0.0/1751.150.0.1 to 51.150.127.25451.150.127.25532,766
4651.150.128.0/1751.150.128.1 to 51.150.255.25451.150.255.25532,766
4751.151.0.0/1751.151.0.1 to 51.151.127.25451.151.127.25532,766
4851.151.128.0/1751.151.128.1 to 51.151.255.25451.151.255.25532,766
4951.152.0.0/1751.152.0.1 to 51.152.127.25451.152.127.25532,766
5051.152.128.0/1751.152.128.1 to 51.152.255.25451.152.255.25532,766
5151.153.0.0/1751.153.0.1 to 51.153.127.25451.153.127.25532,766
5251.153.128.0/1751.153.128.1 to 51.153.255.25451.153.255.25532,766
5351.154.0.0/1751.154.0.1 to 51.154.127.25451.154.127.25532,766
5451.154.128.0/1751.154.128.1 to 51.154.255.25451.154.255.25532,766
5551.155.0.0/1751.155.0.1 to 51.155.127.25451.155.127.25532,766
5651.155.128.0/1751.155.128.1 to 51.155.255.25451.155.255.25532,766
5751.156.0.0/1751.156.0.1 to 51.156.127.25451.156.127.25532,766
5851.156.128.0/1751.156.128.1 to 51.156.255.25451.156.255.25532,766
5951.157.0.0/1751.157.0.1 to 51.157.127.25451.157.127.25532,766
6051.157.128.0/1751.157.128.1 to 51.157.255.25451.157.255.25532,766
6151.158.0.0/1751.158.0.1 to 51.158.127.25451.158.127.25532,766
6251.158.128.0/1751.158.128.1 to 51.158.255.25451.158.255.25532,766
6351.159.0.0/1751.159.0.1 to 51.159.127.25451.159.127.25532,766
6451.159.128.0/1751.159.128.1 to 51.159.255.25451.159.255.25532,766
6551.160.0.0/1751.160.0.1 to 51.160.127.25451.160.127.25532,766
6651.160.128.0/1751.160.128.1 to 51.160.255.25451.160.255.25532,766
6751.161.0.0/1751.161.0.1 to 51.161.127.25451.161.127.25532,766
6851.161.128.0/1751.161.128.1 to 51.161.255.25451.161.255.25532,766
6951.162.0.0/1751.162.0.1 to 51.162.127.25451.162.127.25532,766
7051.162.128.0/1751.162.128.1 to 51.162.255.25451.162.255.25532,766
7151.163.0.0/1751.163.0.1 to 51.163.127.25451.163.127.25532,766
7251.163.128.0/1751.163.128.1 to 51.163.255.25451.163.255.25532,766
7351.164.0.0/1751.164.0.1 to 51.164.127.25451.164.127.25532,766
7451.164.128.0/1751.164.128.1 to 51.164.255.25451.164.255.25532,766
7551.165.0.0/1751.165.0.1 to 51.165.127.25451.165.127.25532,766
7651.165.128.0/1751.165.128.1 to 51.165.255.25451.165.255.25532,766
7751.166.0.0/1751.166.0.1 to 51.166.127.25451.166.127.25532,766
7851.166.128.0/1751.166.128.1 to 51.166.255.25451.166.255.25532,766
7951.167.0.0/1751.167.0.1 to 51.167.127.25451.167.127.25532,766
8051.167.128.0/1751.167.128.1 to 51.167.255.25451.167.255.25532,766
8151.168.0.0/1751.168.0.1 to 51.168.127.25451.168.127.25532,766
8251.168.128.0/1751.168.128.1 to 51.168.255.25451.168.255.25532,766
8351.169.0.0/1751.169.0.1 to 51.169.127.25451.169.127.25532,766
8451.169.128.0/1751.169.128.1 to 51.169.255.25451.169.255.25532,766
8551.170.0.0/1751.170.0.1 to 51.170.127.25451.170.127.25532,766
8651.170.128.0/1751.170.128.1 to 51.170.255.25451.170.255.25532,766
8751.171.0.0/1751.171.0.1 to 51.171.127.25451.171.127.25532,766
8851.171.128.0/1751.171.128.1 to 51.171.255.25451.171.255.25532,766
8951.172.0.0/1751.172.0.1 to 51.172.127.25451.172.127.25532,766
9051.172.128.0/1751.172.128.1 to 51.172.255.25451.172.255.25532,766
9151.173.0.0/1751.173.0.1 to 51.173.127.25451.173.127.25532,766
9251.173.128.0/1751.173.128.1 to 51.173.255.25451.173.255.25532,766
9351.174.0.0/1751.174.0.1 to 51.174.127.25451.174.127.25532,766
9451.174.128.0/1751.174.128.1 to 51.174.255.25451.174.255.25532,766
9551.175.0.0/1751.175.0.1 to 51.175.127.25451.175.127.25532,766
9651.175.128.0/1751.175.128.1 to 51.175.255.25451.175.255.25532,766
9751.176.0.0/1751.176.0.1 to 51.176.127.25451.176.127.25532,766
9851.176.128.0/1751.176.128.1 to 51.176.255.25451.176.255.25532,766
9951.177.0.0/1751.177.0.1 to 51.177.127.25451.177.127.25532,766
10051.177.128.0/1751.177.128.1 to 51.177.255.25451.177.255.25532,766
10151.178.0.0/1751.178.0.1 to 51.178.127.25451.178.127.25532,766
10251.178.128.0/1751.178.128.1 to 51.178.255.25451.178.255.25532,766
10351.179.0.0/1751.179.0.1 to 51.179.127.25451.179.127.25532,766
10451.179.128.0/1751.179.128.1 to 51.179.255.25451.179.255.25532,766
10551.180.0.0/1751.180.0.1 to 51.180.127.25451.180.127.25532,766
10651.180.128.0/1751.180.128.1 to 51.180.255.25451.180.255.25532,766
10751.181.0.0/1751.181.0.1 to 51.181.127.25451.181.127.25532,766
10851.181.128.0/1751.181.128.1 to 51.181.255.25451.181.255.25532,766
10951.182.0.0/1751.182.0.1 to 51.182.127.25451.182.127.25532,766
11051.182.128.0/1751.182.128.1 to 51.182.255.25451.182.255.25532,766
11151.183.0.0/1751.183.0.1 to 51.183.127.25451.183.127.25532,766
11251.183.128.0/1751.183.128.1 to 51.183.255.25451.183.255.25532,766
11351.184.0.0/1751.184.0.1 to 51.184.127.25451.184.127.25532,766
11451.184.128.0/1751.184.128.1 to 51.184.255.25451.184.255.25532,766
11551.185.0.0/1751.185.0.1 to 51.185.127.25451.185.127.25532,766
11651.185.128.0/1751.185.128.1 to 51.185.255.25451.185.255.25532,766
11751.186.0.0/1751.186.0.1 to 51.186.127.25451.186.127.25532,766
11851.186.128.0/1751.186.128.1 to 51.186.255.25451.186.255.25532,766
11951.187.0.0/1751.187.0.1 to 51.187.127.25451.187.127.25532,766
12051.187.128.0/1751.187.128.1 to 51.187.255.25451.187.255.25532,766
12151.188.0.0/1751.188.0.1 to 51.188.127.25451.188.127.25532,766
12251.188.128.0/1751.188.128.1 to 51.188.255.25451.188.255.25532,766
12351.189.0.0/1751.189.0.1 to 51.189.127.25451.189.127.25532,766
12451.189.128.0/1751.189.128.1 to 51.189.255.25451.189.255.25532,766
12551.190.0.0/1751.190.0.1 to 51.190.127.25451.190.127.25532,766
12651.190.128.0/1751.190.128.1 to 51.190.255.25451.190.255.25532,766
12751.191.0.0/1751.191.0.1 to 51.191.127.25451.191.127.25532,766
12851.191.128.0/1751.191.128.1 to 51.191.255.25451.191.255.25532,766

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.