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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.

Network37.128.0.0/9
Usable hosts8,388,606
Subnet mask255.128.0.0
Addresses8,388,608
Network address
37.128.0.0
Broadcast address
37.255.255.255
First usable
37.128.0.1
Last usable
37.255.255.254
Usable hosts
8,388,606 (8,388,608 less the network and broadcast addresses)
Subnet mask
255.128.0.0
Wildcard mask
0.127.255.255 (Cisco ACLs, OSPF)
Prefix length
/9
Type
Public public
Old class
A (default /8)
As numbers
Hex 25800000 · Integer 629145600 to 637534207
Reverse DNS zones
128.37.in-addr.arpa
129.37.in-addr.arpa
130.37.in-addr.arpa
131.37.in-addr.arpa
132.37.in-addr.arpa
133.37.in-addr.arpa
134.37.in-addr.arpa
135.37.in-addr.arpa
136.37.in-addr.arpa
137.37.in-addr.arpa
138.37.in-addr.arpa
139.37.in-addr.arpa
140.37.in-addr.arpa
141.37.in-addr.arpa
142.37.in-addr.arpa
143.37.in-addr.arpa
and 112 more
/9 is not on a 8-bit boundary, so it takes 128 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00100101.10000000.00000000.0000000037.128.0.0
Subnet mask11111111.10000000.00000000.00000000255.128.0.0
Network00100101.10000000.00000000.0000000037.128.0.0
Broadcast00100101.11111111.11111111.1111111137.255.255.255
Split into smaller subnets/16
/10 (2)/11 (4)/12 (8)/13 (16)/14 (32)/15 (64)/16 (128)/17 (256)/18 (512)/19 (1,024)/20 (2,048)/21 (4,096)

37.128.0.0/9 makes 128 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
137.128.0.0/1637.128.0.1 to 37.128.255.25437.128.255.25565,534
237.129.0.0/1637.129.0.1 to 37.129.255.25437.129.255.25565,534
337.130.0.0/1637.130.0.1 to 37.130.255.25437.130.255.25565,534
437.131.0.0/1637.131.0.1 to 37.131.255.25437.131.255.25565,534
537.132.0.0/1637.132.0.1 to 37.132.255.25437.132.255.25565,534
637.133.0.0/1637.133.0.1 to 37.133.255.25437.133.255.25565,534
737.134.0.0/1637.134.0.1 to 37.134.255.25437.134.255.25565,534
837.135.0.0/1637.135.0.1 to 37.135.255.25437.135.255.25565,534
937.136.0.0/1637.136.0.1 to 37.136.255.25437.136.255.25565,534
1037.137.0.0/1637.137.0.1 to 37.137.255.25437.137.255.25565,534
1137.138.0.0/1637.138.0.1 to 37.138.255.25437.138.255.25565,534
1237.139.0.0/1637.139.0.1 to 37.139.255.25437.139.255.25565,534
1337.140.0.0/1637.140.0.1 to 37.140.255.25437.140.255.25565,534
1437.141.0.0/1637.141.0.1 to 37.141.255.25437.141.255.25565,534
1537.142.0.0/1637.142.0.1 to 37.142.255.25437.142.255.25565,534
1637.143.0.0/1637.143.0.1 to 37.143.255.25437.143.255.25565,534
1737.144.0.0/1637.144.0.1 to 37.144.255.25437.144.255.25565,534
1837.145.0.0/1637.145.0.1 to 37.145.255.25437.145.255.25565,534
1937.146.0.0/1637.146.0.1 to 37.146.255.25437.146.255.25565,534
2037.147.0.0/1637.147.0.1 to 37.147.255.25437.147.255.25565,534
2137.148.0.0/1637.148.0.1 to 37.148.255.25437.148.255.25565,534
2237.149.0.0/1637.149.0.1 to 37.149.255.25437.149.255.25565,534
2337.150.0.0/1637.150.0.1 to 37.150.255.25437.150.255.25565,534
2437.151.0.0/1637.151.0.1 to 37.151.255.25437.151.255.25565,534
2537.152.0.0/1637.152.0.1 to 37.152.255.25437.152.255.25565,534
2637.153.0.0/1637.153.0.1 to 37.153.255.25437.153.255.25565,534
2737.154.0.0/1637.154.0.1 to 37.154.255.25437.154.255.25565,534
2837.155.0.0/1637.155.0.1 to 37.155.255.25437.155.255.25565,534
2937.156.0.0/1637.156.0.1 to 37.156.255.25437.156.255.25565,534
3037.157.0.0/1637.157.0.1 to 37.157.255.25437.157.255.25565,534
3137.158.0.0/1637.158.0.1 to 37.158.255.25437.158.255.25565,534
3237.159.0.0/1637.159.0.1 to 37.159.255.25437.159.255.25565,534
3337.160.0.0/1637.160.0.1 to 37.160.255.25437.160.255.25565,534
3437.161.0.0/1637.161.0.1 to 37.161.255.25437.161.255.25565,534
3537.162.0.0/1637.162.0.1 to 37.162.255.25437.162.255.25565,534
3637.163.0.0/1637.163.0.1 to 37.163.255.25437.163.255.25565,534
3737.164.0.0/1637.164.0.1 to 37.164.255.25437.164.255.25565,534
3837.165.0.0/1637.165.0.1 to 37.165.255.25437.165.255.25565,534
3937.166.0.0/1637.166.0.1 to 37.166.255.25437.166.255.25565,534
4037.167.0.0/1637.167.0.1 to 37.167.255.25437.167.255.25565,534
4137.168.0.0/1637.168.0.1 to 37.168.255.25437.168.255.25565,534
4237.169.0.0/1637.169.0.1 to 37.169.255.25437.169.255.25565,534
4337.170.0.0/1637.170.0.1 to 37.170.255.25437.170.255.25565,534
4437.171.0.0/1637.171.0.1 to 37.171.255.25437.171.255.25565,534
4537.172.0.0/1637.172.0.1 to 37.172.255.25437.172.255.25565,534
4637.173.0.0/1637.173.0.1 to 37.173.255.25437.173.255.25565,534
4737.174.0.0/1637.174.0.1 to 37.174.255.25437.174.255.25565,534
4837.175.0.0/1637.175.0.1 to 37.175.255.25437.175.255.25565,534
4937.176.0.0/1637.176.0.1 to 37.176.255.25437.176.255.25565,534
5037.177.0.0/1637.177.0.1 to 37.177.255.25437.177.255.25565,534
5137.178.0.0/1637.178.0.1 to 37.178.255.25437.178.255.25565,534
5237.179.0.0/1637.179.0.1 to 37.179.255.25437.179.255.25565,534
5337.180.0.0/1637.180.0.1 to 37.180.255.25437.180.255.25565,534
5437.181.0.0/1637.181.0.1 to 37.181.255.25437.181.255.25565,534
5537.182.0.0/1637.182.0.1 to 37.182.255.25437.182.255.25565,534
5637.183.0.0/1637.183.0.1 to 37.183.255.25437.183.255.25565,534
5737.184.0.0/1637.184.0.1 to 37.184.255.25437.184.255.25565,534
5837.185.0.0/1637.185.0.1 to 37.185.255.25437.185.255.25565,534
5937.186.0.0/1637.186.0.1 to 37.186.255.25437.186.255.25565,534
6037.187.0.0/1637.187.0.1 to 37.187.255.25437.187.255.25565,534
6137.188.0.0/1637.188.0.1 to 37.188.255.25437.188.255.25565,534
6237.189.0.0/1637.189.0.1 to 37.189.255.25437.189.255.25565,534
6337.190.0.0/1637.190.0.1 to 37.190.255.25437.190.255.25565,534
6437.191.0.0/1637.191.0.1 to 37.191.255.25437.191.255.25565,534
6537.192.0.0/1637.192.0.1 to 37.192.255.25437.192.255.25565,534
6637.193.0.0/1637.193.0.1 to 37.193.255.25437.193.255.25565,534
6737.194.0.0/1637.194.0.1 to 37.194.255.25437.194.255.25565,534
6837.195.0.0/1637.195.0.1 to 37.195.255.25437.195.255.25565,534
6937.196.0.0/1637.196.0.1 to 37.196.255.25437.196.255.25565,534
7037.197.0.0/1637.197.0.1 to 37.197.255.25437.197.255.25565,534
7137.198.0.0/1637.198.0.1 to 37.198.255.25437.198.255.25565,534
7237.199.0.0/1637.199.0.1 to 37.199.255.25437.199.255.25565,534
7337.200.0.0/1637.200.0.1 to 37.200.255.25437.200.255.25565,534
7437.201.0.0/1637.201.0.1 to 37.201.255.25437.201.255.25565,534
7537.202.0.0/1637.202.0.1 to 37.202.255.25437.202.255.25565,534
7637.203.0.0/1637.203.0.1 to 37.203.255.25437.203.255.25565,534
7737.204.0.0/1637.204.0.1 to 37.204.255.25437.204.255.25565,534
7837.205.0.0/1637.205.0.1 to 37.205.255.25437.205.255.25565,534
7937.206.0.0/1637.206.0.1 to 37.206.255.25437.206.255.25565,534
8037.207.0.0/1637.207.0.1 to 37.207.255.25437.207.255.25565,534
8137.208.0.0/1637.208.0.1 to 37.208.255.25437.208.255.25565,534
8237.209.0.0/1637.209.0.1 to 37.209.255.25437.209.255.25565,534
8337.210.0.0/1637.210.0.1 to 37.210.255.25437.210.255.25565,534
8437.211.0.0/1637.211.0.1 to 37.211.255.25437.211.255.25565,534
8537.212.0.0/1637.212.0.1 to 37.212.255.25437.212.255.25565,534
8637.213.0.0/1637.213.0.1 to 37.213.255.25437.213.255.25565,534
8737.214.0.0/1637.214.0.1 to 37.214.255.25437.214.255.25565,534
8837.215.0.0/1637.215.0.1 to 37.215.255.25437.215.255.25565,534
8937.216.0.0/1637.216.0.1 to 37.216.255.25437.216.255.25565,534
9037.217.0.0/1637.217.0.1 to 37.217.255.25437.217.255.25565,534
9137.218.0.0/1637.218.0.1 to 37.218.255.25437.218.255.25565,534
9237.219.0.0/1637.219.0.1 to 37.219.255.25437.219.255.25565,534
9337.220.0.0/1637.220.0.1 to 37.220.255.25437.220.255.25565,534
9437.221.0.0/1637.221.0.1 to 37.221.255.25437.221.255.25565,534
9537.222.0.0/1637.222.0.1 to 37.222.255.25437.222.255.25565,534
9637.223.0.0/1637.223.0.1 to 37.223.255.25437.223.255.25565,534
9737.224.0.0/1637.224.0.1 to 37.224.255.25437.224.255.25565,534
9837.225.0.0/1637.225.0.1 to 37.225.255.25437.225.255.25565,534
9937.226.0.0/1637.226.0.1 to 37.226.255.25437.226.255.25565,534
10037.227.0.0/1637.227.0.1 to 37.227.255.25437.227.255.25565,534
10137.228.0.0/1637.228.0.1 to 37.228.255.25437.228.255.25565,534
10237.229.0.0/1637.229.0.1 to 37.229.255.25437.229.255.25565,534
10337.230.0.0/1637.230.0.1 to 37.230.255.25437.230.255.25565,534
10437.231.0.0/1637.231.0.1 to 37.231.255.25437.231.255.25565,534
10537.232.0.0/1637.232.0.1 to 37.232.255.25437.232.255.25565,534
10637.233.0.0/1637.233.0.1 to 37.233.255.25437.233.255.25565,534
10737.234.0.0/1637.234.0.1 to 37.234.255.25437.234.255.25565,534
10837.235.0.0/1637.235.0.1 to 37.235.255.25437.235.255.25565,534
10937.236.0.0/1637.236.0.1 to 37.236.255.25437.236.255.25565,534
11037.237.0.0/1637.237.0.1 to 37.237.255.25437.237.255.25565,534
11137.238.0.0/1637.238.0.1 to 37.238.255.25437.238.255.25565,534
11237.239.0.0/1637.239.0.1 to 37.239.255.25437.239.255.25565,534
11337.240.0.0/1637.240.0.1 to 37.240.255.25437.240.255.25565,534
11437.241.0.0/1637.241.0.1 to 37.241.255.25437.241.255.25565,534
11537.242.0.0/1637.242.0.1 to 37.242.255.25437.242.255.25565,534
11637.243.0.0/1637.243.0.1 to 37.243.255.25437.243.255.25565,534
11737.244.0.0/1637.244.0.1 to 37.244.255.25437.244.255.25565,534
11837.245.0.0/1637.245.0.1 to 37.245.255.25437.245.255.25565,534
11937.246.0.0/1637.246.0.1 to 37.246.255.25437.246.255.25565,534
12037.247.0.0/1637.247.0.1 to 37.247.255.25437.247.255.25565,534
12137.248.0.0/1637.248.0.1 to 37.248.255.25437.248.255.25565,534
12237.249.0.0/1637.249.0.1 to 37.249.255.25437.249.255.25565,534
12337.250.0.0/1637.250.0.1 to 37.250.255.25437.250.255.25565,534
12437.251.0.0/1637.251.0.1 to 37.251.255.25437.251.255.25565,534
12537.252.0.0/1637.252.0.1 to 37.252.255.25437.252.255.25565,534
12637.253.0.0/1637.253.0.1 to 37.253.255.25437.253.255.25565,534
12737.254.0.0/1637.254.0.1 to 37.254.255.25437.254.255.25565,534
12837.255.0.0/1637.255.0.1 to 37.255.255.25437.255.255.25565,534

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.