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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.

Network187.4.16.0/20
Usable hosts4,094
Subnet mask255.255.240.0
Addresses4,096
Network address
187.4.16.0
Broadcast address
187.4.31.255
First usable
187.4.16.1
Last usable
187.4.31.254
Usable hosts
4,094 (4,096 less the network and broadcast addresses)
Subnet mask
255.255.240.0
Wildcard mask
0.0.15.255 (Cisco ACLs, OSPF)
Prefix length
/20
Type
Public public
Old class
B (default /16)
As numbers
Hex BB041000 · Integer 3137605632 to 3137609727
Reverse DNS zones
16.4.187.in-addr.arpa
17.4.187.in-addr.arpa
18.4.187.in-addr.arpa
19.4.187.in-addr.arpa
20.4.187.in-addr.arpa
21.4.187.in-addr.arpa
22.4.187.in-addr.arpa
23.4.187.in-addr.arpa
24.4.187.in-addr.arpa
25.4.187.in-addr.arpa
26.4.187.in-addr.arpa
27.4.187.in-addr.arpa
28.4.187.in-addr.arpa
29.4.187.in-addr.arpa
30.4.187.in-addr.arpa
31.4.187.in-addr.arpa
/20 is not on a 8-bit boundary, so it takes 16 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10111011.00000100.00010000.00000000187.4.16.0
Subnet mask11111111.11111111.11110000.00000000255.255.240.0
Network10111011.00000100.00010000.00000000187.4.16.0
Broadcast10111011.00000100.00011111.11111111187.4.31.255
Split into smaller subnets/27
/21 (2)/22 (4)/23 (8)/24 (16)/25 (32)/26 (64)/27 (128)/28 (256)/29 (512)/30 (1,024)/31 (2,048)/32 (4,096)

187.4.16.0/20 makes 128 subnets of /27.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1187.4.16.0/27187.4.16.1 to 187.4.16.30187.4.16.3130
2187.4.16.32/27187.4.16.33 to 187.4.16.62187.4.16.6330
3187.4.16.64/27187.4.16.65 to 187.4.16.94187.4.16.9530
4187.4.16.96/27187.4.16.97 to 187.4.16.126187.4.16.12730
5187.4.16.128/27187.4.16.129 to 187.4.16.158187.4.16.15930
6187.4.16.160/27187.4.16.161 to 187.4.16.190187.4.16.19130
7187.4.16.192/27187.4.16.193 to 187.4.16.222187.4.16.22330
8187.4.16.224/27187.4.16.225 to 187.4.16.254187.4.16.25530
9187.4.17.0/27187.4.17.1 to 187.4.17.30187.4.17.3130
10187.4.17.32/27187.4.17.33 to 187.4.17.62187.4.17.6330
11187.4.17.64/27187.4.17.65 to 187.4.17.94187.4.17.9530
12187.4.17.96/27187.4.17.97 to 187.4.17.126187.4.17.12730
13187.4.17.128/27187.4.17.129 to 187.4.17.158187.4.17.15930
14187.4.17.160/27187.4.17.161 to 187.4.17.190187.4.17.19130
15187.4.17.192/27187.4.17.193 to 187.4.17.222187.4.17.22330
16187.4.17.224/27187.4.17.225 to 187.4.17.254187.4.17.25530
17187.4.18.0/27187.4.18.1 to 187.4.18.30187.4.18.3130
18187.4.18.32/27187.4.18.33 to 187.4.18.62187.4.18.6330
19187.4.18.64/27187.4.18.65 to 187.4.18.94187.4.18.9530
20187.4.18.96/27187.4.18.97 to 187.4.18.126187.4.18.12730
21187.4.18.128/27187.4.18.129 to 187.4.18.158187.4.18.15930
22187.4.18.160/27187.4.18.161 to 187.4.18.190187.4.18.19130
23187.4.18.192/27187.4.18.193 to 187.4.18.222187.4.18.22330
24187.4.18.224/27187.4.18.225 to 187.4.18.254187.4.18.25530
25187.4.19.0/27187.4.19.1 to 187.4.19.30187.4.19.3130
26187.4.19.32/27187.4.19.33 to 187.4.19.62187.4.19.6330
27187.4.19.64/27187.4.19.65 to 187.4.19.94187.4.19.9530
28187.4.19.96/27187.4.19.97 to 187.4.19.126187.4.19.12730
29187.4.19.128/27187.4.19.129 to 187.4.19.158187.4.19.15930
30187.4.19.160/27187.4.19.161 to 187.4.19.190187.4.19.19130
31187.4.19.192/27187.4.19.193 to 187.4.19.222187.4.19.22330
32187.4.19.224/27187.4.19.225 to 187.4.19.254187.4.19.25530
33187.4.20.0/27187.4.20.1 to 187.4.20.30187.4.20.3130
34187.4.20.32/27187.4.20.33 to 187.4.20.62187.4.20.6330
35187.4.20.64/27187.4.20.65 to 187.4.20.94187.4.20.9530
36187.4.20.96/27187.4.20.97 to 187.4.20.126187.4.20.12730
37187.4.20.128/27187.4.20.129 to 187.4.20.158187.4.20.15930
38187.4.20.160/27187.4.20.161 to 187.4.20.190187.4.20.19130
39187.4.20.192/27187.4.20.193 to 187.4.20.222187.4.20.22330
40187.4.20.224/27187.4.20.225 to 187.4.20.254187.4.20.25530
41187.4.21.0/27187.4.21.1 to 187.4.21.30187.4.21.3130
42187.4.21.32/27187.4.21.33 to 187.4.21.62187.4.21.6330
43187.4.21.64/27187.4.21.65 to 187.4.21.94187.4.21.9530
44187.4.21.96/27187.4.21.97 to 187.4.21.126187.4.21.12730
45187.4.21.128/27187.4.21.129 to 187.4.21.158187.4.21.15930
46187.4.21.160/27187.4.21.161 to 187.4.21.190187.4.21.19130
47187.4.21.192/27187.4.21.193 to 187.4.21.222187.4.21.22330
48187.4.21.224/27187.4.21.225 to 187.4.21.254187.4.21.25530
49187.4.22.0/27187.4.22.1 to 187.4.22.30187.4.22.3130
50187.4.22.32/27187.4.22.33 to 187.4.22.62187.4.22.6330
51187.4.22.64/27187.4.22.65 to 187.4.22.94187.4.22.9530
52187.4.22.96/27187.4.22.97 to 187.4.22.126187.4.22.12730
53187.4.22.128/27187.4.22.129 to 187.4.22.158187.4.22.15930
54187.4.22.160/27187.4.22.161 to 187.4.22.190187.4.22.19130
55187.4.22.192/27187.4.22.193 to 187.4.22.222187.4.22.22330
56187.4.22.224/27187.4.22.225 to 187.4.22.254187.4.22.25530
57187.4.23.0/27187.4.23.1 to 187.4.23.30187.4.23.3130
58187.4.23.32/27187.4.23.33 to 187.4.23.62187.4.23.6330
59187.4.23.64/27187.4.23.65 to 187.4.23.94187.4.23.9530
60187.4.23.96/27187.4.23.97 to 187.4.23.126187.4.23.12730
61187.4.23.128/27187.4.23.129 to 187.4.23.158187.4.23.15930
62187.4.23.160/27187.4.23.161 to 187.4.23.190187.4.23.19130
63187.4.23.192/27187.4.23.193 to 187.4.23.222187.4.23.22330
64187.4.23.224/27187.4.23.225 to 187.4.23.254187.4.23.25530
65187.4.24.0/27187.4.24.1 to 187.4.24.30187.4.24.3130
66187.4.24.32/27187.4.24.33 to 187.4.24.62187.4.24.6330
67187.4.24.64/27187.4.24.65 to 187.4.24.94187.4.24.9530
68187.4.24.96/27187.4.24.97 to 187.4.24.126187.4.24.12730
69187.4.24.128/27187.4.24.129 to 187.4.24.158187.4.24.15930
70187.4.24.160/27187.4.24.161 to 187.4.24.190187.4.24.19130
71187.4.24.192/27187.4.24.193 to 187.4.24.222187.4.24.22330
72187.4.24.224/27187.4.24.225 to 187.4.24.254187.4.24.25530
73187.4.25.0/27187.4.25.1 to 187.4.25.30187.4.25.3130
74187.4.25.32/27187.4.25.33 to 187.4.25.62187.4.25.6330
75187.4.25.64/27187.4.25.65 to 187.4.25.94187.4.25.9530
76187.4.25.96/27187.4.25.97 to 187.4.25.126187.4.25.12730
77187.4.25.128/27187.4.25.129 to 187.4.25.158187.4.25.15930
78187.4.25.160/27187.4.25.161 to 187.4.25.190187.4.25.19130
79187.4.25.192/27187.4.25.193 to 187.4.25.222187.4.25.22330
80187.4.25.224/27187.4.25.225 to 187.4.25.254187.4.25.25530
81187.4.26.0/27187.4.26.1 to 187.4.26.30187.4.26.3130
82187.4.26.32/27187.4.26.33 to 187.4.26.62187.4.26.6330
83187.4.26.64/27187.4.26.65 to 187.4.26.94187.4.26.9530
84187.4.26.96/27187.4.26.97 to 187.4.26.126187.4.26.12730
85187.4.26.128/27187.4.26.129 to 187.4.26.158187.4.26.15930
86187.4.26.160/27187.4.26.161 to 187.4.26.190187.4.26.19130
87187.4.26.192/27187.4.26.193 to 187.4.26.222187.4.26.22330
88187.4.26.224/27187.4.26.225 to 187.4.26.254187.4.26.25530
89187.4.27.0/27187.4.27.1 to 187.4.27.30187.4.27.3130
90187.4.27.32/27187.4.27.33 to 187.4.27.62187.4.27.6330
91187.4.27.64/27187.4.27.65 to 187.4.27.94187.4.27.9530
92187.4.27.96/27187.4.27.97 to 187.4.27.126187.4.27.12730
93187.4.27.128/27187.4.27.129 to 187.4.27.158187.4.27.15930
94187.4.27.160/27187.4.27.161 to 187.4.27.190187.4.27.19130
95187.4.27.192/27187.4.27.193 to 187.4.27.222187.4.27.22330
96187.4.27.224/27187.4.27.225 to 187.4.27.254187.4.27.25530
97187.4.28.0/27187.4.28.1 to 187.4.28.30187.4.28.3130
98187.4.28.32/27187.4.28.33 to 187.4.28.62187.4.28.6330
99187.4.28.64/27187.4.28.65 to 187.4.28.94187.4.28.9530
100187.4.28.96/27187.4.28.97 to 187.4.28.126187.4.28.12730
101187.4.28.128/27187.4.28.129 to 187.4.28.158187.4.28.15930
102187.4.28.160/27187.4.28.161 to 187.4.28.190187.4.28.19130
103187.4.28.192/27187.4.28.193 to 187.4.28.222187.4.28.22330
104187.4.28.224/27187.4.28.225 to 187.4.28.254187.4.28.25530
105187.4.29.0/27187.4.29.1 to 187.4.29.30187.4.29.3130
106187.4.29.32/27187.4.29.33 to 187.4.29.62187.4.29.6330
107187.4.29.64/27187.4.29.65 to 187.4.29.94187.4.29.9530
108187.4.29.96/27187.4.29.97 to 187.4.29.126187.4.29.12730
109187.4.29.128/27187.4.29.129 to 187.4.29.158187.4.29.15930
110187.4.29.160/27187.4.29.161 to 187.4.29.190187.4.29.19130
111187.4.29.192/27187.4.29.193 to 187.4.29.222187.4.29.22330
112187.4.29.224/27187.4.29.225 to 187.4.29.254187.4.29.25530
113187.4.30.0/27187.4.30.1 to 187.4.30.30187.4.30.3130
114187.4.30.32/27187.4.30.33 to 187.4.30.62187.4.30.6330
115187.4.30.64/27187.4.30.65 to 187.4.30.94187.4.30.9530
116187.4.30.96/27187.4.30.97 to 187.4.30.126187.4.30.12730
117187.4.30.128/27187.4.30.129 to 187.4.30.158187.4.30.15930
118187.4.30.160/27187.4.30.161 to 187.4.30.190187.4.30.19130
119187.4.30.192/27187.4.30.193 to 187.4.30.222187.4.30.22330
120187.4.30.224/27187.4.30.225 to 187.4.30.254187.4.30.25530
121187.4.31.0/27187.4.31.1 to 187.4.31.30187.4.31.3130
122187.4.31.32/27187.4.31.33 to 187.4.31.62187.4.31.6330
123187.4.31.64/27187.4.31.65 to 187.4.31.94187.4.31.9530
124187.4.31.96/27187.4.31.97 to 187.4.31.126187.4.31.12730
125187.4.31.128/27187.4.31.129 to 187.4.31.158187.4.31.15930
126187.4.31.160/27187.4.31.161 to 187.4.31.190187.4.31.19130
127187.4.31.192/27187.4.31.193 to 187.4.31.222187.4.31.22330
128187.4.31.224/27187.4.31.225 to 187.4.31.254187.4.31.25530

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.