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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.

Network243.7.64.0/18
Usable hosts16,382
Subnet mask255.255.192.0
Addresses16,384
Network address
243.7.64.0
Broadcast address
243.7.127.255
First usable
243.7.64.1
Last usable
243.7.127.254
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
Reserved 240.0.0.0/4
Future use; not usable on most systems
Old class
E (reserved)
As numbers
Hex F3074000 · Integer 4077338624 to 4077355007
Reverse DNS zones
64.7.243.in-addr.arpa
65.7.243.in-addr.arpa
66.7.243.in-addr.arpa
67.7.243.in-addr.arpa
68.7.243.in-addr.arpa
69.7.243.in-addr.arpa
70.7.243.in-addr.arpa
71.7.243.in-addr.arpa
72.7.243.in-addr.arpa
73.7.243.in-addr.arpa
74.7.243.in-addr.arpa
75.7.243.in-addr.arpa
76.7.243.in-addr.arpa
77.7.243.in-addr.arpa
78.7.243.in-addr.arpa
79.7.243.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
Address11110011.00000111.01000000.00000000243.7.64.0
Subnet mask11111111.11111111.11000000.00000000255.255.192.0
Network11110011.00000111.01000000.00000000243.7.64.0
Broadcast11110011.00000111.01111111.11111111243.7.127.255
Split into smaller subnets/25
/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)

243.7.64.0/18 makes 128 subnets of /25.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1243.7.64.0/25243.7.64.1 to 243.7.64.126243.7.64.127126
2243.7.64.128/25243.7.64.129 to 243.7.64.254243.7.64.255126
3243.7.65.0/25243.7.65.1 to 243.7.65.126243.7.65.127126
4243.7.65.128/25243.7.65.129 to 243.7.65.254243.7.65.255126
5243.7.66.0/25243.7.66.1 to 243.7.66.126243.7.66.127126
6243.7.66.128/25243.7.66.129 to 243.7.66.254243.7.66.255126
7243.7.67.0/25243.7.67.1 to 243.7.67.126243.7.67.127126
8243.7.67.128/25243.7.67.129 to 243.7.67.254243.7.67.255126
9243.7.68.0/25243.7.68.1 to 243.7.68.126243.7.68.127126
10243.7.68.128/25243.7.68.129 to 243.7.68.254243.7.68.255126
11243.7.69.0/25243.7.69.1 to 243.7.69.126243.7.69.127126
12243.7.69.128/25243.7.69.129 to 243.7.69.254243.7.69.255126
13243.7.70.0/25243.7.70.1 to 243.7.70.126243.7.70.127126
14243.7.70.128/25243.7.70.129 to 243.7.70.254243.7.70.255126
15243.7.71.0/25243.7.71.1 to 243.7.71.126243.7.71.127126
16243.7.71.128/25243.7.71.129 to 243.7.71.254243.7.71.255126
17243.7.72.0/25243.7.72.1 to 243.7.72.126243.7.72.127126
18243.7.72.128/25243.7.72.129 to 243.7.72.254243.7.72.255126
19243.7.73.0/25243.7.73.1 to 243.7.73.126243.7.73.127126
20243.7.73.128/25243.7.73.129 to 243.7.73.254243.7.73.255126
21243.7.74.0/25243.7.74.1 to 243.7.74.126243.7.74.127126
22243.7.74.128/25243.7.74.129 to 243.7.74.254243.7.74.255126
23243.7.75.0/25243.7.75.1 to 243.7.75.126243.7.75.127126
24243.7.75.128/25243.7.75.129 to 243.7.75.254243.7.75.255126
25243.7.76.0/25243.7.76.1 to 243.7.76.126243.7.76.127126
26243.7.76.128/25243.7.76.129 to 243.7.76.254243.7.76.255126
27243.7.77.0/25243.7.77.1 to 243.7.77.126243.7.77.127126
28243.7.77.128/25243.7.77.129 to 243.7.77.254243.7.77.255126
29243.7.78.0/25243.7.78.1 to 243.7.78.126243.7.78.127126
30243.7.78.128/25243.7.78.129 to 243.7.78.254243.7.78.255126
31243.7.79.0/25243.7.79.1 to 243.7.79.126243.7.79.127126
32243.7.79.128/25243.7.79.129 to 243.7.79.254243.7.79.255126
33243.7.80.0/25243.7.80.1 to 243.7.80.126243.7.80.127126
34243.7.80.128/25243.7.80.129 to 243.7.80.254243.7.80.255126
35243.7.81.0/25243.7.81.1 to 243.7.81.126243.7.81.127126
36243.7.81.128/25243.7.81.129 to 243.7.81.254243.7.81.255126
37243.7.82.0/25243.7.82.1 to 243.7.82.126243.7.82.127126
38243.7.82.128/25243.7.82.129 to 243.7.82.254243.7.82.255126
39243.7.83.0/25243.7.83.1 to 243.7.83.126243.7.83.127126
40243.7.83.128/25243.7.83.129 to 243.7.83.254243.7.83.255126
41243.7.84.0/25243.7.84.1 to 243.7.84.126243.7.84.127126
42243.7.84.128/25243.7.84.129 to 243.7.84.254243.7.84.255126
43243.7.85.0/25243.7.85.1 to 243.7.85.126243.7.85.127126
44243.7.85.128/25243.7.85.129 to 243.7.85.254243.7.85.255126
45243.7.86.0/25243.7.86.1 to 243.7.86.126243.7.86.127126
46243.7.86.128/25243.7.86.129 to 243.7.86.254243.7.86.255126
47243.7.87.0/25243.7.87.1 to 243.7.87.126243.7.87.127126
48243.7.87.128/25243.7.87.129 to 243.7.87.254243.7.87.255126
49243.7.88.0/25243.7.88.1 to 243.7.88.126243.7.88.127126
50243.7.88.128/25243.7.88.129 to 243.7.88.254243.7.88.255126
51243.7.89.0/25243.7.89.1 to 243.7.89.126243.7.89.127126
52243.7.89.128/25243.7.89.129 to 243.7.89.254243.7.89.255126
53243.7.90.0/25243.7.90.1 to 243.7.90.126243.7.90.127126
54243.7.90.128/25243.7.90.129 to 243.7.90.254243.7.90.255126
55243.7.91.0/25243.7.91.1 to 243.7.91.126243.7.91.127126
56243.7.91.128/25243.7.91.129 to 243.7.91.254243.7.91.255126
57243.7.92.0/25243.7.92.1 to 243.7.92.126243.7.92.127126
58243.7.92.128/25243.7.92.129 to 243.7.92.254243.7.92.255126
59243.7.93.0/25243.7.93.1 to 243.7.93.126243.7.93.127126
60243.7.93.128/25243.7.93.129 to 243.7.93.254243.7.93.255126
61243.7.94.0/25243.7.94.1 to 243.7.94.126243.7.94.127126
62243.7.94.128/25243.7.94.129 to 243.7.94.254243.7.94.255126
63243.7.95.0/25243.7.95.1 to 243.7.95.126243.7.95.127126
64243.7.95.128/25243.7.95.129 to 243.7.95.254243.7.95.255126
65243.7.96.0/25243.7.96.1 to 243.7.96.126243.7.96.127126
66243.7.96.128/25243.7.96.129 to 243.7.96.254243.7.96.255126
67243.7.97.0/25243.7.97.1 to 243.7.97.126243.7.97.127126
68243.7.97.128/25243.7.97.129 to 243.7.97.254243.7.97.255126
69243.7.98.0/25243.7.98.1 to 243.7.98.126243.7.98.127126
70243.7.98.128/25243.7.98.129 to 243.7.98.254243.7.98.255126
71243.7.99.0/25243.7.99.1 to 243.7.99.126243.7.99.127126
72243.7.99.128/25243.7.99.129 to 243.7.99.254243.7.99.255126
73243.7.100.0/25243.7.100.1 to 243.7.100.126243.7.100.127126
74243.7.100.128/25243.7.100.129 to 243.7.100.254243.7.100.255126
75243.7.101.0/25243.7.101.1 to 243.7.101.126243.7.101.127126
76243.7.101.128/25243.7.101.129 to 243.7.101.254243.7.101.255126
77243.7.102.0/25243.7.102.1 to 243.7.102.126243.7.102.127126
78243.7.102.128/25243.7.102.129 to 243.7.102.254243.7.102.255126
79243.7.103.0/25243.7.103.1 to 243.7.103.126243.7.103.127126
80243.7.103.128/25243.7.103.129 to 243.7.103.254243.7.103.255126
81243.7.104.0/25243.7.104.1 to 243.7.104.126243.7.104.127126
82243.7.104.128/25243.7.104.129 to 243.7.104.254243.7.104.255126
83243.7.105.0/25243.7.105.1 to 243.7.105.126243.7.105.127126
84243.7.105.128/25243.7.105.129 to 243.7.105.254243.7.105.255126
85243.7.106.0/25243.7.106.1 to 243.7.106.126243.7.106.127126
86243.7.106.128/25243.7.106.129 to 243.7.106.254243.7.106.255126
87243.7.107.0/25243.7.107.1 to 243.7.107.126243.7.107.127126
88243.7.107.128/25243.7.107.129 to 243.7.107.254243.7.107.255126
89243.7.108.0/25243.7.108.1 to 243.7.108.126243.7.108.127126
90243.7.108.128/25243.7.108.129 to 243.7.108.254243.7.108.255126
91243.7.109.0/25243.7.109.1 to 243.7.109.126243.7.109.127126
92243.7.109.128/25243.7.109.129 to 243.7.109.254243.7.109.255126
93243.7.110.0/25243.7.110.1 to 243.7.110.126243.7.110.127126
94243.7.110.128/25243.7.110.129 to 243.7.110.254243.7.110.255126
95243.7.111.0/25243.7.111.1 to 243.7.111.126243.7.111.127126
96243.7.111.128/25243.7.111.129 to 243.7.111.254243.7.111.255126
97243.7.112.0/25243.7.112.1 to 243.7.112.126243.7.112.127126
98243.7.112.128/25243.7.112.129 to 243.7.112.254243.7.112.255126
99243.7.113.0/25243.7.113.1 to 243.7.113.126243.7.113.127126
100243.7.113.128/25243.7.113.129 to 243.7.113.254243.7.113.255126
101243.7.114.0/25243.7.114.1 to 243.7.114.126243.7.114.127126
102243.7.114.128/25243.7.114.129 to 243.7.114.254243.7.114.255126
103243.7.115.0/25243.7.115.1 to 243.7.115.126243.7.115.127126
104243.7.115.128/25243.7.115.129 to 243.7.115.254243.7.115.255126
105243.7.116.0/25243.7.116.1 to 243.7.116.126243.7.116.127126
106243.7.116.128/25243.7.116.129 to 243.7.116.254243.7.116.255126
107243.7.117.0/25243.7.117.1 to 243.7.117.126243.7.117.127126
108243.7.117.128/25243.7.117.129 to 243.7.117.254243.7.117.255126
109243.7.118.0/25243.7.118.1 to 243.7.118.126243.7.118.127126
110243.7.118.128/25243.7.118.129 to 243.7.118.254243.7.118.255126
111243.7.119.0/25243.7.119.1 to 243.7.119.126243.7.119.127126
112243.7.119.128/25243.7.119.129 to 243.7.119.254243.7.119.255126
113243.7.120.0/25243.7.120.1 to 243.7.120.126243.7.120.127126
114243.7.120.128/25243.7.120.129 to 243.7.120.254243.7.120.255126
115243.7.121.0/25243.7.121.1 to 243.7.121.126243.7.121.127126
116243.7.121.128/25243.7.121.129 to 243.7.121.254243.7.121.255126
117243.7.122.0/25243.7.122.1 to 243.7.122.126243.7.122.127126
118243.7.122.128/25243.7.122.129 to 243.7.122.254243.7.122.255126
119243.7.123.0/25243.7.123.1 to 243.7.123.126243.7.123.127126
120243.7.123.128/25243.7.123.129 to 243.7.123.254243.7.123.255126
121243.7.124.0/25243.7.124.1 to 243.7.124.126243.7.124.127126
122243.7.124.128/25243.7.124.129 to 243.7.124.254243.7.124.255126
123243.7.125.0/25243.7.125.1 to 243.7.125.126243.7.125.127126
124243.7.125.128/25243.7.125.129 to 243.7.125.254243.7.125.255126
125243.7.126.0/25243.7.126.1 to 243.7.126.126243.7.126.127126
126243.7.126.128/25243.7.126.129 to 243.7.126.254243.7.126.255126
127243.7.127.0/25243.7.127.1 to 243.7.127.126243.7.127.127126
128243.7.127.128/25243.7.127.129 to 243.7.127.254243.7.127.255126

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.