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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.

Network221.2.128.0/19
Usable hosts8,190
Subnet mask255.255.224.0
Addresses8,192
Network address
221.2.128.0
Broadcast address
221.2.159.255
First usable
221.2.128.1
Last usable
221.2.159.254
Usable hosts
8,190 (8,192 less the network and broadcast addresses)
Subnet mask
255.255.224.0
Wildcard mask
0.0.31.255 (Cisco ACLs, OSPF)
Prefix length
/19
Type
Public public
Old class
C (default /24)
As numbers
Hex DD028000 · Integer 3707928576 to 3707936767
Reverse DNS zones
128.2.221.in-addr.arpa
129.2.221.in-addr.arpa
130.2.221.in-addr.arpa
131.2.221.in-addr.arpa
132.2.221.in-addr.arpa
133.2.221.in-addr.arpa
134.2.221.in-addr.arpa
135.2.221.in-addr.arpa
136.2.221.in-addr.arpa
137.2.221.in-addr.arpa
138.2.221.in-addr.arpa
139.2.221.in-addr.arpa
140.2.221.in-addr.arpa
141.2.221.in-addr.arpa
142.2.221.in-addr.arpa
143.2.221.in-addr.arpa
and 16 more
/19 is not on a 8-bit boundary, so it takes 32 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11011101.00000010.10000000.00000000221.2.128.0
Subnet mask11111111.11111111.11100000.00000000255.255.224.0
Network11011101.00000010.10000000.00000000221.2.128.0
Broadcast11011101.00000010.10011111.11111111221.2.159.255
Split into smaller subnets/26
/20 (2)/21 (4)/22 (8)/23 (16)/24 (32)/25 (64)/26 (128)/27 (256)/28 (512)/29 (1,024)/30 (2,048)/31 (4,096)

221.2.128.0/19 makes 128 subnets of /26.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1221.2.128.0/26221.2.128.1 to 221.2.128.62221.2.128.6362
2221.2.128.64/26221.2.128.65 to 221.2.128.126221.2.128.12762
3221.2.128.128/26221.2.128.129 to 221.2.128.190221.2.128.19162
4221.2.128.192/26221.2.128.193 to 221.2.128.254221.2.128.25562
5221.2.129.0/26221.2.129.1 to 221.2.129.62221.2.129.6362
6221.2.129.64/26221.2.129.65 to 221.2.129.126221.2.129.12762
7221.2.129.128/26221.2.129.129 to 221.2.129.190221.2.129.19162
8221.2.129.192/26221.2.129.193 to 221.2.129.254221.2.129.25562
9221.2.130.0/26221.2.130.1 to 221.2.130.62221.2.130.6362
10221.2.130.64/26221.2.130.65 to 221.2.130.126221.2.130.12762
11221.2.130.128/26221.2.130.129 to 221.2.130.190221.2.130.19162
12221.2.130.192/26221.2.130.193 to 221.2.130.254221.2.130.25562
13221.2.131.0/26221.2.131.1 to 221.2.131.62221.2.131.6362
14221.2.131.64/26221.2.131.65 to 221.2.131.126221.2.131.12762
15221.2.131.128/26221.2.131.129 to 221.2.131.190221.2.131.19162
16221.2.131.192/26221.2.131.193 to 221.2.131.254221.2.131.25562
17221.2.132.0/26221.2.132.1 to 221.2.132.62221.2.132.6362
18221.2.132.64/26221.2.132.65 to 221.2.132.126221.2.132.12762
19221.2.132.128/26221.2.132.129 to 221.2.132.190221.2.132.19162
20221.2.132.192/26221.2.132.193 to 221.2.132.254221.2.132.25562
21221.2.133.0/26221.2.133.1 to 221.2.133.62221.2.133.6362
22221.2.133.64/26221.2.133.65 to 221.2.133.126221.2.133.12762
23221.2.133.128/26221.2.133.129 to 221.2.133.190221.2.133.19162
24221.2.133.192/26221.2.133.193 to 221.2.133.254221.2.133.25562
25221.2.134.0/26221.2.134.1 to 221.2.134.62221.2.134.6362
26221.2.134.64/26221.2.134.65 to 221.2.134.126221.2.134.12762
27221.2.134.128/26221.2.134.129 to 221.2.134.190221.2.134.19162
28221.2.134.192/26221.2.134.193 to 221.2.134.254221.2.134.25562
29221.2.135.0/26221.2.135.1 to 221.2.135.62221.2.135.6362
30221.2.135.64/26221.2.135.65 to 221.2.135.126221.2.135.12762
31221.2.135.128/26221.2.135.129 to 221.2.135.190221.2.135.19162
32221.2.135.192/26221.2.135.193 to 221.2.135.254221.2.135.25562
33221.2.136.0/26221.2.136.1 to 221.2.136.62221.2.136.6362
34221.2.136.64/26221.2.136.65 to 221.2.136.126221.2.136.12762
35221.2.136.128/26221.2.136.129 to 221.2.136.190221.2.136.19162
36221.2.136.192/26221.2.136.193 to 221.2.136.254221.2.136.25562
37221.2.137.0/26221.2.137.1 to 221.2.137.62221.2.137.6362
38221.2.137.64/26221.2.137.65 to 221.2.137.126221.2.137.12762
39221.2.137.128/26221.2.137.129 to 221.2.137.190221.2.137.19162
40221.2.137.192/26221.2.137.193 to 221.2.137.254221.2.137.25562
41221.2.138.0/26221.2.138.1 to 221.2.138.62221.2.138.6362
42221.2.138.64/26221.2.138.65 to 221.2.138.126221.2.138.12762
43221.2.138.128/26221.2.138.129 to 221.2.138.190221.2.138.19162
44221.2.138.192/26221.2.138.193 to 221.2.138.254221.2.138.25562
45221.2.139.0/26221.2.139.1 to 221.2.139.62221.2.139.6362
46221.2.139.64/26221.2.139.65 to 221.2.139.126221.2.139.12762
47221.2.139.128/26221.2.139.129 to 221.2.139.190221.2.139.19162
48221.2.139.192/26221.2.139.193 to 221.2.139.254221.2.139.25562
49221.2.140.0/26221.2.140.1 to 221.2.140.62221.2.140.6362
50221.2.140.64/26221.2.140.65 to 221.2.140.126221.2.140.12762
51221.2.140.128/26221.2.140.129 to 221.2.140.190221.2.140.19162
52221.2.140.192/26221.2.140.193 to 221.2.140.254221.2.140.25562
53221.2.141.0/26221.2.141.1 to 221.2.141.62221.2.141.6362
54221.2.141.64/26221.2.141.65 to 221.2.141.126221.2.141.12762
55221.2.141.128/26221.2.141.129 to 221.2.141.190221.2.141.19162
56221.2.141.192/26221.2.141.193 to 221.2.141.254221.2.141.25562
57221.2.142.0/26221.2.142.1 to 221.2.142.62221.2.142.6362
58221.2.142.64/26221.2.142.65 to 221.2.142.126221.2.142.12762
59221.2.142.128/26221.2.142.129 to 221.2.142.190221.2.142.19162
60221.2.142.192/26221.2.142.193 to 221.2.142.254221.2.142.25562
61221.2.143.0/26221.2.143.1 to 221.2.143.62221.2.143.6362
62221.2.143.64/26221.2.143.65 to 221.2.143.126221.2.143.12762
63221.2.143.128/26221.2.143.129 to 221.2.143.190221.2.143.19162
64221.2.143.192/26221.2.143.193 to 221.2.143.254221.2.143.25562
65221.2.144.0/26221.2.144.1 to 221.2.144.62221.2.144.6362
66221.2.144.64/26221.2.144.65 to 221.2.144.126221.2.144.12762
67221.2.144.128/26221.2.144.129 to 221.2.144.190221.2.144.19162
68221.2.144.192/26221.2.144.193 to 221.2.144.254221.2.144.25562
69221.2.145.0/26221.2.145.1 to 221.2.145.62221.2.145.6362
70221.2.145.64/26221.2.145.65 to 221.2.145.126221.2.145.12762
71221.2.145.128/26221.2.145.129 to 221.2.145.190221.2.145.19162
72221.2.145.192/26221.2.145.193 to 221.2.145.254221.2.145.25562
73221.2.146.0/26221.2.146.1 to 221.2.146.62221.2.146.6362
74221.2.146.64/26221.2.146.65 to 221.2.146.126221.2.146.12762
75221.2.146.128/26221.2.146.129 to 221.2.146.190221.2.146.19162
76221.2.146.192/26221.2.146.193 to 221.2.146.254221.2.146.25562
77221.2.147.0/26221.2.147.1 to 221.2.147.62221.2.147.6362
78221.2.147.64/26221.2.147.65 to 221.2.147.126221.2.147.12762
79221.2.147.128/26221.2.147.129 to 221.2.147.190221.2.147.19162
80221.2.147.192/26221.2.147.193 to 221.2.147.254221.2.147.25562
81221.2.148.0/26221.2.148.1 to 221.2.148.62221.2.148.6362
82221.2.148.64/26221.2.148.65 to 221.2.148.126221.2.148.12762
83221.2.148.128/26221.2.148.129 to 221.2.148.190221.2.148.19162
84221.2.148.192/26221.2.148.193 to 221.2.148.254221.2.148.25562
85221.2.149.0/26221.2.149.1 to 221.2.149.62221.2.149.6362
86221.2.149.64/26221.2.149.65 to 221.2.149.126221.2.149.12762
87221.2.149.128/26221.2.149.129 to 221.2.149.190221.2.149.19162
88221.2.149.192/26221.2.149.193 to 221.2.149.254221.2.149.25562
89221.2.150.0/26221.2.150.1 to 221.2.150.62221.2.150.6362
90221.2.150.64/26221.2.150.65 to 221.2.150.126221.2.150.12762
91221.2.150.128/26221.2.150.129 to 221.2.150.190221.2.150.19162
92221.2.150.192/26221.2.150.193 to 221.2.150.254221.2.150.25562
93221.2.151.0/26221.2.151.1 to 221.2.151.62221.2.151.6362
94221.2.151.64/26221.2.151.65 to 221.2.151.126221.2.151.12762
95221.2.151.128/26221.2.151.129 to 221.2.151.190221.2.151.19162
96221.2.151.192/26221.2.151.193 to 221.2.151.254221.2.151.25562
97221.2.152.0/26221.2.152.1 to 221.2.152.62221.2.152.6362
98221.2.152.64/26221.2.152.65 to 221.2.152.126221.2.152.12762
99221.2.152.128/26221.2.152.129 to 221.2.152.190221.2.152.19162
100221.2.152.192/26221.2.152.193 to 221.2.152.254221.2.152.25562
101221.2.153.0/26221.2.153.1 to 221.2.153.62221.2.153.6362
102221.2.153.64/26221.2.153.65 to 221.2.153.126221.2.153.12762
103221.2.153.128/26221.2.153.129 to 221.2.153.190221.2.153.19162
104221.2.153.192/26221.2.153.193 to 221.2.153.254221.2.153.25562
105221.2.154.0/26221.2.154.1 to 221.2.154.62221.2.154.6362
106221.2.154.64/26221.2.154.65 to 221.2.154.126221.2.154.12762
107221.2.154.128/26221.2.154.129 to 221.2.154.190221.2.154.19162
108221.2.154.192/26221.2.154.193 to 221.2.154.254221.2.154.25562
109221.2.155.0/26221.2.155.1 to 221.2.155.62221.2.155.6362
110221.2.155.64/26221.2.155.65 to 221.2.155.126221.2.155.12762
111221.2.155.128/26221.2.155.129 to 221.2.155.190221.2.155.19162
112221.2.155.192/26221.2.155.193 to 221.2.155.254221.2.155.25562
113221.2.156.0/26221.2.156.1 to 221.2.156.62221.2.156.6362
114221.2.156.64/26221.2.156.65 to 221.2.156.126221.2.156.12762
115221.2.156.128/26221.2.156.129 to 221.2.156.190221.2.156.19162
116221.2.156.192/26221.2.156.193 to 221.2.156.254221.2.156.25562
117221.2.157.0/26221.2.157.1 to 221.2.157.62221.2.157.6362
118221.2.157.64/26221.2.157.65 to 221.2.157.126221.2.157.12762
119221.2.157.128/26221.2.157.129 to 221.2.157.190221.2.157.19162
120221.2.157.192/26221.2.157.193 to 221.2.157.254221.2.157.25562
121221.2.158.0/26221.2.158.1 to 221.2.158.62221.2.158.6362
122221.2.158.64/26221.2.158.65 to 221.2.158.126221.2.158.12762
123221.2.158.128/26221.2.158.129 to 221.2.158.190221.2.158.19162
124221.2.158.192/26221.2.158.193 to 221.2.158.254221.2.158.25562
125221.2.159.0/26221.2.159.1 to 221.2.159.62221.2.159.6362
126221.2.159.64/26221.2.159.65 to 221.2.159.126221.2.159.12762
127221.2.159.128/26221.2.159.129 to 221.2.159.190221.2.159.19162
128221.2.159.192/26221.2.159.193 to 221.2.159.254221.2.159.25562

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.