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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.

Network192.168.160.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
192.168.160.0
Broadcast address
192.168.167.255
First usable
192.168.160.1
Last usable
192.168.167.254
Usable hosts
2,046 (2,048 less the network and broadcast addresses)
Subnet mask
255.255.248.0
Wildcard mask
0.0.7.255 (Cisco ACLs, OSPF)
Prefix length
/21
Type
Private (RFC 1918) 192.168.0.0/16
Office and home networks; not routed on the internet
Old class
C (default /24)
As numbers
Hex C0A8A000 · Integer 3232276480 to 3232278527
Reverse DNS zones
160.168.192.in-addr.arpa
161.168.192.in-addr.arpa
162.168.192.in-addr.arpa
163.168.192.in-addr.arpa
164.168.192.in-addr.arpa
165.168.192.in-addr.arpa
166.168.192.in-addr.arpa
167.168.192.in-addr.arpa
/21 is not on a 8-bit boundary, so it takes 8 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11000000.10101000.10100000.00000000192.168.160.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network11000000.10101000.10100000.00000000192.168.160.0
Broadcast11000000.10101000.10100111.11111111192.168.167.255
Split into smaller subnets/27
/22 (2)/23 (4)/24 (8)/25 (16)/26 (32)/27 (64)/28 (128)/29 (256)/30 (512)/31 (1,024)/32 (2,048)

192.168.160.0/21 makes 64 subnets of /27.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1192.168.160.0/27192.168.160.1 to 192.168.160.30192.168.160.3130
2192.168.160.32/27192.168.160.33 to 192.168.160.62192.168.160.6330
3192.168.160.64/27192.168.160.65 to 192.168.160.94192.168.160.9530
4192.168.160.96/27192.168.160.97 to 192.168.160.126192.168.160.12730
5192.168.160.128/27192.168.160.129 to 192.168.160.158192.168.160.15930
6192.168.160.160/27192.168.160.161 to 192.168.160.190192.168.160.19130
7192.168.160.192/27192.168.160.193 to 192.168.160.222192.168.160.22330
8192.168.160.224/27192.168.160.225 to 192.168.160.254192.168.160.25530
9192.168.161.0/27192.168.161.1 to 192.168.161.30192.168.161.3130
10192.168.161.32/27192.168.161.33 to 192.168.161.62192.168.161.6330
11192.168.161.64/27192.168.161.65 to 192.168.161.94192.168.161.9530
12192.168.161.96/27192.168.161.97 to 192.168.161.126192.168.161.12730
13192.168.161.128/27192.168.161.129 to 192.168.161.158192.168.161.15930
14192.168.161.160/27192.168.161.161 to 192.168.161.190192.168.161.19130
15192.168.161.192/27192.168.161.193 to 192.168.161.222192.168.161.22330
16192.168.161.224/27192.168.161.225 to 192.168.161.254192.168.161.25530
17192.168.162.0/27192.168.162.1 to 192.168.162.30192.168.162.3130
18192.168.162.32/27192.168.162.33 to 192.168.162.62192.168.162.6330
19192.168.162.64/27192.168.162.65 to 192.168.162.94192.168.162.9530
20192.168.162.96/27192.168.162.97 to 192.168.162.126192.168.162.12730
21192.168.162.128/27192.168.162.129 to 192.168.162.158192.168.162.15930
22192.168.162.160/27192.168.162.161 to 192.168.162.190192.168.162.19130
23192.168.162.192/27192.168.162.193 to 192.168.162.222192.168.162.22330
24192.168.162.224/27192.168.162.225 to 192.168.162.254192.168.162.25530
25192.168.163.0/27192.168.163.1 to 192.168.163.30192.168.163.3130
26192.168.163.32/27192.168.163.33 to 192.168.163.62192.168.163.6330
27192.168.163.64/27192.168.163.65 to 192.168.163.94192.168.163.9530
28192.168.163.96/27192.168.163.97 to 192.168.163.126192.168.163.12730
29192.168.163.128/27192.168.163.129 to 192.168.163.158192.168.163.15930
30192.168.163.160/27192.168.163.161 to 192.168.163.190192.168.163.19130
31192.168.163.192/27192.168.163.193 to 192.168.163.222192.168.163.22330
32192.168.163.224/27192.168.163.225 to 192.168.163.254192.168.163.25530
33192.168.164.0/27192.168.164.1 to 192.168.164.30192.168.164.3130
34192.168.164.32/27192.168.164.33 to 192.168.164.62192.168.164.6330
35192.168.164.64/27192.168.164.65 to 192.168.164.94192.168.164.9530
36192.168.164.96/27192.168.164.97 to 192.168.164.126192.168.164.12730
37192.168.164.128/27192.168.164.129 to 192.168.164.158192.168.164.15930
38192.168.164.160/27192.168.164.161 to 192.168.164.190192.168.164.19130
39192.168.164.192/27192.168.164.193 to 192.168.164.222192.168.164.22330
40192.168.164.224/27192.168.164.225 to 192.168.164.254192.168.164.25530
41192.168.165.0/27192.168.165.1 to 192.168.165.30192.168.165.3130
42192.168.165.32/27192.168.165.33 to 192.168.165.62192.168.165.6330
43192.168.165.64/27192.168.165.65 to 192.168.165.94192.168.165.9530
44192.168.165.96/27192.168.165.97 to 192.168.165.126192.168.165.12730
45192.168.165.128/27192.168.165.129 to 192.168.165.158192.168.165.15930
46192.168.165.160/27192.168.165.161 to 192.168.165.190192.168.165.19130
47192.168.165.192/27192.168.165.193 to 192.168.165.222192.168.165.22330
48192.168.165.224/27192.168.165.225 to 192.168.165.254192.168.165.25530
49192.168.166.0/27192.168.166.1 to 192.168.166.30192.168.166.3130
50192.168.166.32/27192.168.166.33 to 192.168.166.62192.168.166.6330
51192.168.166.64/27192.168.166.65 to 192.168.166.94192.168.166.9530
52192.168.166.96/27192.168.166.97 to 192.168.166.126192.168.166.12730
53192.168.166.128/27192.168.166.129 to 192.168.166.158192.168.166.15930
54192.168.166.160/27192.168.166.161 to 192.168.166.190192.168.166.19130
55192.168.166.192/27192.168.166.193 to 192.168.166.222192.168.166.22330
56192.168.166.224/27192.168.166.225 to 192.168.166.254192.168.166.25530
57192.168.167.0/27192.168.167.1 to 192.168.167.30192.168.167.3130
58192.168.167.32/27192.168.167.33 to 192.168.167.62192.168.167.6330
59192.168.167.64/27192.168.167.65 to 192.168.167.94192.168.167.9530
60192.168.167.96/27192.168.167.97 to 192.168.167.126192.168.167.12730
61192.168.167.128/27192.168.167.129 to 192.168.167.158192.168.167.15930
62192.168.167.160/27192.168.167.161 to 192.168.167.190192.168.167.19130
63192.168.167.192/27192.168.167.193 to 192.168.167.222192.168.167.22330
64192.168.167.224/27192.168.167.225 to 192.168.167.254192.168.167.25530

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.