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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.

Network187.4.192.0/18
Usable hosts16,382
Subnet mask255.255.192.0
Addresses16,384
Network address
187.4.192.0
Broadcast address
187.4.255.255
First usable
187.4.192.1
Last usable
187.4.255.254
Usable hosts
16,382 (16,384 less the network and broadcast addresses)
Subnet mask
255.255.192.0
Wildcard mask
0.0.63.255 (Cisco ACLs, OSPF)
Prefix length
/18
Type
Public public
Old class
B (default /16)
As numbers
Hex BB04C000 · Integer 3137650688 to 3137667071
Reverse DNS zones
192.4.187.in-addr.arpa
193.4.187.in-addr.arpa
194.4.187.in-addr.arpa
195.4.187.in-addr.arpa
196.4.187.in-addr.arpa
197.4.187.in-addr.arpa
198.4.187.in-addr.arpa
199.4.187.in-addr.arpa
200.4.187.in-addr.arpa
201.4.187.in-addr.arpa
202.4.187.in-addr.arpa
203.4.187.in-addr.arpa
204.4.187.in-addr.arpa
205.4.187.in-addr.arpa
206.4.187.in-addr.arpa
207.4.187.in-addr.arpa
and 48 more
/18 is not on a 8-bit boundary, so it takes 64 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10111011.00000100.11000000.00000000187.4.192.0
Subnet mask11111111.11111111.11000000.00000000255.255.192.0
Network10111011.00000100.11000000.00000000187.4.192.0
Broadcast10111011.00000100.11111111.11111111187.4.255.255
Split into smaller subnets/24
/19 (2)/20 (4)/21 (8)/22 (16)/23 (32)/24 (64)/25 (128)/26 (256)/27 (512)/28 (1,024)/29 (2,048)/30 (4,096)

187.4.192.0/18 makes 64 subnets of /24.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1187.4.192.0/24187.4.192.1 to 187.4.192.254187.4.192.255254
2187.4.193.0/24187.4.193.1 to 187.4.193.254187.4.193.255254
3187.4.194.0/24187.4.194.1 to 187.4.194.254187.4.194.255254
4187.4.195.0/24187.4.195.1 to 187.4.195.254187.4.195.255254
5187.4.196.0/24187.4.196.1 to 187.4.196.254187.4.196.255254
6187.4.197.0/24187.4.197.1 to 187.4.197.254187.4.197.255254
7187.4.198.0/24187.4.198.1 to 187.4.198.254187.4.198.255254
8187.4.199.0/24187.4.199.1 to 187.4.199.254187.4.199.255254
9187.4.200.0/24187.4.200.1 to 187.4.200.254187.4.200.255254
10187.4.201.0/24187.4.201.1 to 187.4.201.254187.4.201.255254
11187.4.202.0/24187.4.202.1 to 187.4.202.254187.4.202.255254
12187.4.203.0/24187.4.203.1 to 187.4.203.254187.4.203.255254
13187.4.204.0/24187.4.204.1 to 187.4.204.254187.4.204.255254
14187.4.205.0/24187.4.205.1 to 187.4.205.254187.4.205.255254
15187.4.206.0/24187.4.206.1 to 187.4.206.254187.4.206.255254
16187.4.207.0/24187.4.207.1 to 187.4.207.254187.4.207.255254
17187.4.208.0/24187.4.208.1 to 187.4.208.254187.4.208.255254
18187.4.209.0/24187.4.209.1 to 187.4.209.254187.4.209.255254
19187.4.210.0/24187.4.210.1 to 187.4.210.254187.4.210.255254
20187.4.211.0/24187.4.211.1 to 187.4.211.254187.4.211.255254
21187.4.212.0/24187.4.212.1 to 187.4.212.254187.4.212.255254
22187.4.213.0/24187.4.213.1 to 187.4.213.254187.4.213.255254
23187.4.214.0/24187.4.214.1 to 187.4.214.254187.4.214.255254
24187.4.215.0/24187.4.215.1 to 187.4.215.254187.4.215.255254
25187.4.216.0/24187.4.216.1 to 187.4.216.254187.4.216.255254
26187.4.217.0/24187.4.217.1 to 187.4.217.254187.4.217.255254
27187.4.218.0/24187.4.218.1 to 187.4.218.254187.4.218.255254
28187.4.219.0/24187.4.219.1 to 187.4.219.254187.4.219.255254
29187.4.220.0/24187.4.220.1 to 187.4.220.254187.4.220.255254
30187.4.221.0/24187.4.221.1 to 187.4.221.254187.4.221.255254
31187.4.222.0/24187.4.222.1 to 187.4.222.254187.4.222.255254
32187.4.223.0/24187.4.223.1 to 187.4.223.254187.4.223.255254
33187.4.224.0/24187.4.224.1 to 187.4.224.254187.4.224.255254
34187.4.225.0/24187.4.225.1 to 187.4.225.254187.4.225.255254
35187.4.226.0/24187.4.226.1 to 187.4.226.254187.4.226.255254
36187.4.227.0/24187.4.227.1 to 187.4.227.254187.4.227.255254
37187.4.228.0/24187.4.228.1 to 187.4.228.254187.4.228.255254
38187.4.229.0/24187.4.229.1 to 187.4.229.254187.4.229.255254
39187.4.230.0/24187.4.230.1 to 187.4.230.254187.4.230.255254
40187.4.231.0/24187.4.231.1 to 187.4.231.254187.4.231.255254
41187.4.232.0/24187.4.232.1 to 187.4.232.254187.4.232.255254
42187.4.233.0/24187.4.233.1 to 187.4.233.254187.4.233.255254
43187.4.234.0/24187.4.234.1 to 187.4.234.254187.4.234.255254
44187.4.235.0/24187.4.235.1 to 187.4.235.254187.4.235.255254
45187.4.236.0/24187.4.236.1 to 187.4.236.254187.4.236.255254
46187.4.237.0/24187.4.237.1 to 187.4.237.254187.4.237.255254
47187.4.238.0/24187.4.238.1 to 187.4.238.254187.4.238.255254
48187.4.239.0/24187.4.239.1 to 187.4.239.254187.4.239.255254
49187.4.240.0/24187.4.240.1 to 187.4.240.254187.4.240.255254
50187.4.241.0/24187.4.241.1 to 187.4.241.254187.4.241.255254
51187.4.242.0/24187.4.242.1 to 187.4.242.254187.4.242.255254
52187.4.243.0/24187.4.243.1 to 187.4.243.254187.4.243.255254
53187.4.244.0/24187.4.244.1 to 187.4.244.254187.4.244.255254
54187.4.245.0/24187.4.245.1 to 187.4.245.254187.4.245.255254
55187.4.246.0/24187.4.246.1 to 187.4.246.254187.4.246.255254
56187.4.247.0/24187.4.247.1 to 187.4.247.254187.4.247.255254
57187.4.248.0/24187.4.248.1 to 187.4.248.254187.4.248.255254
58187.4.249.0/24187.4.249.1 to 187.4.249.254187.4.249.255254
59187.4.250.0/24187.4.250.1 to 187.4.250.254187.4.250.255254
60187.4.251.0/24187.4.251.1 to 187.4.251.254187.4.251.255254
61187.4.252.0/24187.4.252.1 to 187.4.252.254187.4.252.255254
62187.4.253.0/24187.4.253.1 to 187.4.253.254187.4.253.255254
63187.4.254.0/24187.4.254.1 to 187.4.254.254187.4.254.255254
64187.4.255.0/24187.4.255.1 to 187.4.255.254187.4.255.255254

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.