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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.

Network203.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
203.0.0.0
Broadcast address
203.255.255.255
First usable
203.0.0.1
Last usable
203.255.255.254
Usable hosts
16,777,214 (16,777,216 less the network and broadcast addresses)
Subnet mask
255.0.0.0
Wildcard mask
0.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/8
Type
Public public
Old class
C (default /24)
As numbers
Hex CB000000 · Integer 3405774848 to 3422552063
Reverse DNS zone
203.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11001011..00000000.00000000.00000000203.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network11001011..00000000.00000000.00000000203.0.0.0
Broadcast11001011..11111111.11111111.11111111203.255.255.255
Split into smaller subnets/15
/9 (2)/10 (4)/11 (8)/12 (16)/13 (32)/14 (64)/15 (128)/16 (256)/17 (512)/18 (1,024)/19 (2,048)/20 (4,096)

203.0.0.0/8 makes 128 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1203.0.0.0/15203.0.0.1 to 203.1.255.254203.1.255.255131,070
2203.2.0.0/15203.2.0.1 to 203.3.255.254203.3.255.255131,070
3203.4.0.0/15203.4.0.1 to 203.5.255.254203.5.255.255131,070
4203.6.0.0/15203.6.0.1 to 203.7.255.254203.7.255.255131,070
5203.8.0.0/15203.8.0.1 to 203.9.255.254203.9.255.255131,070
6203.10.0.0/15203.10.0.1 to 203.11.255.254203.11.255.255131,070
7203.12.0.0/15203.12.0.1 to 203.13.255.254203.13.255.255131,070
8203.14.0.0/15203.14.0.1 to 203.15.255.254203.15.255.255131,070
9203.16.0.0/15203.16.0.1 to 203.17.255.254203.17.255.255131,070
10203.18.0.0/15203.18.0.1 to 203.19.255.254203.19.255.255131,070
11203.20.0.0/15203.20.0.1 to 203.21.255.254203.21.255.255131,070
12203.22.0.0/15203.22.0.1 to 203.23.255.254203.23.255.255131,070
13203.24.0.0/15203.24.0.1 to 203.25.255.254203.25.255.255131,070
14203.26.0.0/15203.26.0.1 to 203.27.255.254203.27.255.255131,070
15203.28.0.0/15203.28.0.1 to 203.29.255.254203.29.255.255131,070
16203.30.0.0/15203.30.0.1 to 203.31.255.254203.31.255.255131,070
17203.32.0.0/15203.32.0.1 to 203.33.255.254203.33.255.255131,070
18203.34.0.0/15203.34.0.1 to 203.35.255.254203.35.255.255131,070
19203.36.0.0/15203.36.0.1 to 203.37.255.254203.37.255.255131,070
20203.38.0.0/15203.38.0.1 to 203.39.255.254203.39.255.255131,070
21203.40.0.0/15203.40.0.1 to 203.41.255.254203.41.255.255131,070
22203.42.0.0/15203.42.0.1 to 203.43.255.254203.43.255.255131,070
23203.44.0.0/15203.44.0.1 to 203.45.255.254203.45.255.255131,070
24203.46.0.0/15203.46.0.1 to 203.47.255.254203.47.255.255131,070
25203.48.0.0/15203.48.0.1 to 203.49.255.254203.49.255.255131,070
26203.50.0.0/15203.50.0.1 to 203.51.255.254203.51.255.255131,070
27203.52.0.0/15203.52.0.1 to 203.53.255.254203.53.255.255131,070
28203.54.0.0/15203.54.0.1 to 203.55.255.254203.55.255.255131,070
29203.56.0.0/15203.56.0.1 to 203.57.255.254203.57.255.255131,070
30203.58.0.0/15203.58.0.1 to 203.59.255.254203.59.255.255131,070
31203.60.0.0/15203.60.0.1 to 203.61.255.254203.61.255.255131,070
32203.62.0.0/15203.62.0.1 to 203.63.255.254203.63.255.255131,070
33203.64.0.0/15203.64.0.1 to 203.65.255.254203.65.255.255131,070
34203.66.0.0/15203.66.0.1 to 203.67.255.254203.67.255.255131,070
35203.68.0.0/15203.68.0.1 to 203.69.255.254203.69.255.255131,070
36203.70.0.0/15203.70.0.1 to 203.71.255.254203.71.255.255131,070
37203.72.0.0/15203.72.0.1 to 203.73.255.254203.73.255.255131,070
38203.74.0.0/15203.74.0.1 to 203.75.255.254203.75.255.255131,070
39203.76.0.0/15203.76.0.1 to 203.77.255.254203.77.255.255131,070
40203.78.0.0/15203.78.0.1 to 203.79.255.254203.79.255.255131,070
41203.80.0.0/15203.80.0.1 to 203.81.255.254203.81.255.255131,070
42203.82.0.0/15203.82.0.1 to 203.83.255.254203.83.255.255131,070
43203.84.0.0/15203.84.0.1 to 203.85.255.254203.85.255.255131,070
44203.86.0.0/15203.86.0.1 to 203.87.255.254203.87.255.255131,070
45203.88.0.0/15203.88.0.1 to 203.89.255.254203.89.255.255131,070
46203.90.0.0/15203.90.0.1 to 203.91.255.254203.91.255.255131,070
47203.92.0.0/15203.92.0.1 to 203.93.255.254203.93.255.255131,070
48203.94.0.0/15203.94.0.1 to 203.95.255.254203.95.255.255131,070
49203.96.0.0/15203.96.0.1 to 203.97.255.254203.97.255.255131,070
50203.98.0.0/15203.98.0.1 to 203.99.255.254203.99.255.255131,070
51203.100.0.0/15203.100.0.1 to 203.101.255.254203.101.255.255131,070
52203.102.0.0/15203.102.0.1 to 203.103.255.254203.103.255.255131,070
53203.104.0.0/15203.104.0.1 to 203.105.255.254203.105.255.255131,070
54203.106.0.0/15203.106.0.1 to 203.107.255.254203.107.255.255131,070
55203.108.0.0/15203.108.0.1 to 203.109.255.254203.109.255.255131,070
56203.110.0.0/15203.110.0.1 to 203.111.255.254203.111.255.255131,070
57203.112.0.0/15203.112.0.1 to 203.113.255.254203.113.255.255131,070
58203.114.0.0/15203.114.0.1 to 203.115.255.254203.115.255.255131,070
59203.116.0.0/15203.116.0.1 to 203.117.255.254203.117.255.255131,070
60203.118.0.0/15203.118.0.1 to 203.119.255.254203.119.255.255131,070
61203.120.0.0/15203.120.0.1 to 203.121.255.254203.121.255.255131,070
62203.122.0.0/15203.122.0.1 to 203.123.255.254203.123.255.255131,070
63203.124.0.0/15203.124.0.1 to 203.125.255.254203.125.255.255131,070
64203.126.0.0/15203.126.0.1 to 203.127.255.254203.127.255.255131,070
65203.128.0.0/15203.128.0.1 to 203.129.255.254203.129.255.255131,070
66203.130.0.0/15203.130.0.1 to 203.131.255.254203.131.255.255131,070
67203.132.0.0/15203.132.0.1 to 203.133.255.254203.133.255.255131,070
68203.134.0.0/15203.134.0.1 to 203.135.255.254203.135.255.255131,070
69203.136.0.0/15203.136.0.1 to 203.137.255.254203.137.255.255131,070
70203.138.0.0/15203.138.0.1 to 203.139.255.254203.139.255.255131,070
71203.140.0.0/15203.140.0.1 to 203.141.255.254203.141.255.255131,070
72203.142.0.0/15203.142.0.1 to 203.143.255.254203.143.255.255131,070
73203.144.0.0/15203.144.0.1 to 203.145.255.254203.145.255.255131,070
74203.146.0.0/15203.146.0.1 to 203.147.255.254203.147.255.255131,070
75203.148.0.0/15203.148.0.1 to 203.149.255.254203.149.255.255131,070
76203.150.0.0/15203.150.0.1 to 203.151.255.254203.151.255.255131,070
77203.152.0.0/15203.152.0.1 to 203.153.255.254203.153.255.255131,070
78203.154.0.0/15203.154.0.1 to 203.155.255.254203.155.255.255131,070
79203.156.0.0/15203.156.0.1 to 203.157.255.254203.157.255.255131,070
80203.158.0.0/15203.158.0.1 to 203.159.255.254203.159.255.255131,070
81203.160.0.0/15203.160.0.1 to 203.161.255.254203.161.255.255131,070
82203.162.0.0/15203.162.0.1 to 203.163.255.254203.163.255.255131,070
83203.164.0.0/15203.164.0.1 to 203.165.255.254203.165.255.255131,070
84203.166.0.0/15203.166.0.1 to 203.167.255.254203.167.255.255131,070
85203.168.0.0/15203.168.0.1 to 203.169.255.254203.169.255.255131,070
86203.170.0.0/15203.170.0.1 to 203.171.255.254203.171.255.255131,070
87203.172.0.0/15203.172.0.1 to 203.173.255.254203.173.255.255131,070
88203.174.0.0/15203.174.0.1 to 203.175.255.254203.175.255.255131,070
89203.176.0.0/15203.176.0.1 to 203.177.255.254203.177.255.255131,070
90203.178.0.0/15203.178.0.1 to 203.179.255.254203.179.255.255131,070
91203.180.0.0/15203.180.0.1 to 203.181.255.254203.181.255.255131,070
92203.182.0.0/15203.182.0.1 to 203.183.255.254203.183.255.255131,070
93203.184.0.0/15203.184.0.1 to 203.185.255.254203.185.255.255131,070
94203.186.0.0/15203.186.0.1 to 203.187.255.254203.187.255.255131,070
95203.188.0.0/15203.188.0.1 to 203.189.255.254203.189.255.255131,070
96203.190.0.0/15203.190.0.1 to 203.191.255.254203.191.255.255131,070
97203.192.0.0/15203.192.0.1 to 203.193.255.254203.193.255.255131,070
98203.194.0.0/15203.194.0.1 to 203.195.255.254203.195.255.255131,070
99203.196.0.0/15203.196.0.1 to 203.197.255.254203.197.255.255131,070
100203.198.0.0/15203.198.0.1 to 203.199.255.254203.199.255.255131,070
101203.200.0.0/15203.200.0.1 to 203.201.255.254203.201.255.255131,070
102203.202.0.0/15203.202.0.1 to 203.203.255.254203.203.255.255131,070
103203.204.0.0/15203.204.0.1 to 203.205.255.254203.205.255.255131,070
104203.206.0.0/15203.206.0.1 to 203.207.255.254203.207.255.255131,070
105203.208.0.0/15203.208.0.1 to 203.209.255.254203.209.255.255131,070
106203.210.0.0/15203.210.0.1 to 203.211.255.254203.211.255.255131,070
107203.212.0.0/15203.212.0.1 to 203.213.255.254203.213.255.255131,070
108203.214.0.0/15203.214.0.1 to 203.215.255.254203.215.255.255131,070
109203.216.0.0/15203.216.0.1 to 203.217.255.254203.217.255.255131,070
110203.218.0.0/15203.218.0.1 to 203.219.255.254203.219.255.255131,070
111203.220.0.0/15203.220.0.1 to 203.221.255.254203.221.255.255131,070
112203.222.0.0/15203.222.0.1 to 203.223.255.254203.223.255.255131,070
113203.224.0.0/15203.224.0.1 to 203.225.255.254203.225.255.255131,070
114203.226.0.0/15203.226.0.1 to 203.227.255.254203.227.255.255131,070
115203.228.0.0/15203.228.0.1 to 203.229.255.254203.229.255.255131,070
116203.230.0.0/15203.230.0.1 to 203.231.255.254203.231.255.255131,070
117203.232.0.0/15203.232.0.1 to 203.233.255.254203.233.255.255131,070
118203.234.0.0/15203.234.0.1 to 203.235.255.254203.235.255.255131,070
119203.236.0.0/15203.236.0.1 to 203.237.255.254203.237.255.255131,070
120203.238.0.0/15203.238.0.1 to 203.239.255.254203.239.255.255131,070
121203.240.0.0/15203.240.0.1 to 203.241.255.254203.241.255.255131,070
122203.242.0.0/15203.242.0.1 to 203.243.255.254203.243.255.255131,070
123203.244.0.0/15203.244.0.1 to 203.245.255.254203.245.255.255131,070
124203.246.0.0/15203.246.0.1 to 203.247.255.254203.247.255.255131,070
125203.248.0.0/15203.248.0.1 to 203.249.255.254203.249.255.255131,070
126203.250.0.0/15203.250.0.1 to 203.251.255.254203.251.255.255131,070
127203.252.0.0/15203.252.0.1 to 203.253.255.254203.253.255.255131,070
128203.254.0.0/15203.254.0.1 to 203.255.255.254203.255.255.255131,070

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.