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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.

Network12.240.0.0/12
Usable hosts1,048,574
Subnet mask255.240.0.0
Addresses1,048,576
Network address
12.240.0.0
Broadcast address
12.255.255.255
First usable
12.240.0.1
Last usable
12.255.255.254
Usable hosts
1,048,574 (1,048,576 less the network and broadcast addresses)
Subnet mask
255.240.0.0
Wildcard mask
0.15.255.255 (Cisco ACLs, OSPF)
Prefix length
/12
Type
Public public
Old class
A (default /8)
As numbers
Hex 0CF00000 · Integer 217055232 to 218103807
Reverse DNS zones
240.12.in-addr.arpa
241.12.in-addr.arpa
242.12.in-addr.arpa
243.12.in-addr.arpa
244.12.in-addr.arpa
245.12.in-addr.arpa
246.12.in-addr.arpa
247.12.in-addr.arpa
248.12.in-addr.arpa
249.12.in-addr.arpa
250.12.in-addr.arpa
251.12.in-addr.arpa
252.12.in-addr.arpa
253.12.in-addr.arpa
254.12.in-addr.arpa
255.12.in-addr.arpa
/12 is not on a 8-bit boundary, so it takes 16 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00001100.11110000.00000000.0000000012.240.0.0
Subnet mask11111111.11110000.00000000.00000000255.240.0.0
Network00001100.11110000.00000000.0000000012.240.0.0
Broadcast00001100.11111111.11111111.1111111112.255.255.255
Split into smaller subnets/19
/13 (2)/14 (4)/15 (8)/16 (16)/17 (32)/18 (64)/19 (128)/20 (256)/21 (512)/22 (1,024)/23 (2,048)/24 (4,096)

12.240.0.0/12 makes 128 subnets of /19.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
112.240.0.0/1912.240.0.1 to 12.240.31.25412.240.31.2558,190
212.240.32.0/1912.240.32.1 to 12.240.63.25412.240.63.2558,190
312.240.64.0/1912.240.64.1 to 12.240.95.25412.240.95.2558,190
412.240.96.0/1912.240.96.1 to 12.240.127.25412.240.127.2558,190
512.240.128.0/1912.240.128.1 to 12.240.159.25412.240.159.2558,190
612.240.160.0/1912.240.160.1 to 12.240.191.25412.240.191.2558,190
712.240.192.0/1912.240.192.1 to 12.240.223.25412.240.223.2558,190
812.240.224.0/1912.240.224.1 to 12.240.255.25412.240.255.2558,190
912.241.0.0/1912.241.0.1 to 12.241.31.25412.241.31.2558,190
1012.241.32.0/1912.241.32.1 to 12.241.63.25412.241.63.2558,190
1112.241.64.0/1912.241.64.1 to 12.241.95.25412.241.95.2558,190
1212.241.96.0/1912.241.96.1 to 12.241.127.25412.241.127.2558,190
1312.241.128.0/1912.241.128.1 to 12.241.159.25412.241.159.2558,190
1412.241.160.0/1912.241.160.1 to 12.241.191.25412.241.191.2558,190
1512.241.192.0/1912.241.192.1 to 12.241.223.25412.241.223.2558,190
1612.241.224.0/1912.241.224.1 to 12.241.255.25412.241.255.2558,190
1712.242.0.0/1912.242.0.1 to 12.242.31.25412.242.31.2558,190
1812.242.32.0/1912.242.32.1 to 12.242.63.25412.242.63.2558,190
1912.242.64.0/1912.242.64.1 to 12.242.95.25412.242.95.2558,190
2012.242.96.0/1912.242.96.1 to 12.242.127.25412.242.127.2558,190
2112.242.128.0/1912.242.128.1 to 12.242.159.25412.242.159.2558,190
2212.242.160.0/1912.242.160.1 to 12.242.191.25412.242.191.2558,190
2312.242.192.0/1912.242.192.1 to 12.242.223.25412.242.223.2558,190
2412.242.224.0/1912.242.224.1 to 12.242.255.25412.242.255.2558,190
2512.243.0.0/1912.243.0.1 to 12.243.31.25412.243.31.2558,190
2612.243.32.0/1912.243.32.1 to 12.243.63.25412.243.63.2558,190
2712.243.64.0/1912.243.64.1 to 12.243.95.25412.243.95.2558,190
2812.243.96.0/1912.243.96.1 to 12.243.127.25412.243.127.2558,190
2912.243.128.0/1912.243.128.1 to 12.243.159.25412.243.159.2558,190
3012.243.160.0/1912.243.160.1 to 12.243.191.25412.243.191.2558,190
3112.243.192.0/1912.243.192.1 to 12.243.223.25412.243.223.2558,190
3212.243.224.0/1912.243.224.1 to 12.243.255.25412.243.255.2558,190
3312.244.0.0/1912.244.0.1 to 12.244.31.25412.244.31.2558,190
3412.244.32.0/1912.244.32.1 to 12.244.63.25412.244.63.2558,190
3512.244.64.0/1912.244.64.1 to 12.244.95.25412.244.95.2558,190
3612.244.96.0/1912.244.96.1 to 12.244.127.25412.244.127.2558,190
3712.244.128.0/1912.244.128.1 to 12.244.159.25412.244.159.2558,190
3812.244.160.0/1912.244.160.1 to 12.244.191.25412.244.191.2558,190
3912.244.192.0/1912.244.192.1 to 12.244.223.25412.244.223.2558,190
4012.244.224.0/1912.244.224.1 to 12.244.255.25412.244.255.2558,190
4112.245.0.0/1912.245.0.1 to 12.245.31.25412.245.31.2558,190
4212.245.32.0/1912.245.32.1 to 12.245.63.25412.245.63.2558,190
4312.245.64.0/1912.245.64.1 to 12.245.95.25412.245.95.2558,190
4412.245.96.0/1912.245.96.1 to 12.245.127.25412.245.127.2558,190
4512.245.128.0/1912.245.128.1 to 12.245.159.25412.245.159.2558,190
4612.245.160.0/1912.245.160.1 to 12.245.191.25412.245.191.2558,190
4712.245.192.0/1912.245.192.1 to 12.245.223.25412.245.223.2558,190
4812.245.224.0/1912.245.224.1 to 12.245.255.25412.245.255.2558,190
4912.246.0.0/1912.246.0.1 to 12.246.31.25412.246.31.2558,190
5012.246.32.0/1912.246.32.1 to 12.246.63.25412.246.63.2558,190
5112.246.64.0/1912.246.64.1 to 12.246.95.25412.246.95.2558,190
5212.246.96.0/1912.246.96.1 to 12.246.127.25412.246.127.2558,190
5312.246.128.0/1912.246.128.1 to 12.246.159.25412.246.159.2558,190
5412.246.160.0/1912.246.160.1 to 12.246.191.25412.246.191.2558,190
5512.246.192.0/1912.246.192.1 to 12.246.223.25412.246.223.2558,190
5612.246.224.0/1912.246.224.1 to 12.246.255.25412.246.255.2558,190
5712.247.0.0/1912.247.0.1 to 12.247.31.25412.247.31.2558,190
5812.247.32.0/1912.247.32.1 to 12.247.63.25412.247.63.2558,190
5912.247.64.0/1912.247.64.1 to 12.247.95.25412.247.95.2558,190
6012.247.96.0/1912.247.96.1 to 12.247.127.25412.247.127.2558,190
6112.247.128.0/1912.247.128.1 to 12.247.159.25412.247.159.2558,190
6212.247.160.0/1912.247.160.1 to 12.247.191.25412.247.191.2558,190
6312.247.192.0/1912.247.192.1 to 12.247.223.25412.247.223.2558,190
6412.247.224.0/1912.247.224.1 to 12.247.255.25412.247.255.2558,190
6512.248.0.0/1912.248.0.1 to 12.248.31.25412.248.31.2558,190
6612.248.32.0/1912.248.32.1 to 12.248.63.25412.248.63.2558,190
6712.248.64.0/1912.248.64.1 to 12.248.95.25412.248.95.2558,190
6812.248.96.0/1912.248.96.1 to 12.248.127.25412.248.127.2558,190
6912.248.128.0/1912.248.128.1 to 12.248.159.25412.248.159.2558,190
7012.248.160.0/1912.248.160.1 to 12.248.191.25412.248.191.2558,190
7112.248.192.0/1912.248.192.1 to 12.248.223.25412.248.223.2558,190
7212.248.224.0/1912.248.224.1 to 12.248.255.25412.248.255.2558,190
7312.249.0.0/1912.249.0.1 to 12.249.31.25412.249.31.2558,190
7412.249.32.0/1912.249.32.1 to 12.249.63.25412.249.63.2558,190
7512.249.64.0/1912.249.64.1 to 12.249.95.25412.249.95.2558,190
7612.249.96.0/1912.249.96.1 to 12.249.127.25412.249.127.2558,190
7712.249.128.0/1912.249.128.1 to 12.249.159.25412.249.159.2558,190
7812.249.160.0/1912.249.160.1 to 12.249.191.25412.249.191.2558,190
7912.249.192.0/1912.249.192.1 to 12.249.223.25412.249.223.2558,190
8012.249.224.0/1912.249.224.1 to 12.249.255.25412.249.255.2558,190
8112.250.0.0/1912.250.0.1 to 12.250.31.25412.250.31.2558,190
8212.250.32.0/1912.250.32.1 to 12.250.63.25412.250.63.2558,190
8312.250.64.0/1912.250.64.1 to 12.250.95.25412.250.95.2558,190
8412.250.96.0/1912.250.96.1 to 12.250.127.25412.250.127.2558,190
8512.250.128.0/1912.250.128.1 to 12.250.159.25412.250.159.2558,190
8612.250.160.0/1912.250.160.1 to 12.250.191.25412.250.191.2558,190
8712.250.192.0/1912.250.192.1 to 12.250.223.25412.250.223.2558,190
8812.250.224.0/1912.250.224.1 to 12.250.255.25412.250.255.2558,190
8912.251.0.0/1912.251.0.1 to 12.251.31.25412.251.31.2558,190
9012.251.32.0/1912.251.32.1 to 12.251.63.25412.251.63.2558,190
9112.251.64.0/1912.251.64.1 to 12.251.95.25412.251.95.2558,190
9212.251.96.0/1912.251.96.1 to 12.251.127.25412.251.127.2558,190
9312.251.128.0/1912.251.128.1 to 12.251.159.25412.251.159.2558,190
9412.251.160.0/1912.251.160.1 to 12.251.191.25412.251.191.2558,190
9512.251.192.0/1912.251.192.1 to 12.251.223.25412.251.223.2558,190
9612.251.224.0/1912.251.224.1 to 12.251.255.25412.251.255.2558,190
9712.252.0.0/1912.252.0.1 to 12.252.31.25412.252.31.2558,190
9812.252.32.0/1912.252.32.1 to 12.252.63.25412.252.63.2558,190
9912.252.64.0/1912.252.64.1 to 12.252.95.25412.252.95.2558,190
10012.252.96.0/1912.252.96.1 to 12.252.127.25412.252.127.2558,190
10112.252.128.0/1912.252.128.1 to 12.252.159.25412.252.159.2558,190
10212.252.160.0/1912.252.160.1 to 12.252.191.25412.252.191.2558,190
10312.252.192.0/1912.252.192.1 to 12.252.223.25412.252.223.2558,190
10412.252.224.0/1912.252.224.1 to 12.252.255.25412.252.255.2558,190
10512.253.0.0/1912.253.0.1 to 12.253.31.25412.253.31.2558,190
10612.253.32.0/1912.253.32.1 to 12.253.63.25412.253.63.2558,190
10712.253.64.0/1912.253.64.1 to 12.253.95.25412.253.95.2558,190
10812.253.96.0/1912.253.96.1 to 12.253.127.25412.253.127.2558,190
10912.253.128.0/1912.253.128.1 to 12.253.159.25412.253.159.2558,190
11012.253.160.0/1912.253.160.1 to 12.253.191.25412.253.191.2558,190
11112.253.192.0/1912.253.192.1 to 12.253.223.25412.253.223.2558,190
11212.253.224.0/1912.253.224.1 to 12.253.255.25412.253.255.2558,190
11312.254.0.0/1912.254.0.1 to 12.254.31.25412.254.31.2558,190
11412.254.32.0/1912.254.32.1 to 12.254.63.25412.254.63.2558,190
11512.254.64.0/1912.254.64.1 to 12.254.95.25412.254.95.2558,190
11612.254.96.0/1912.254.96.1 to 12.254.127.25412.254.127.2558,190
11712.254.128.0/1912.254.128.1 to 12.254.159.25412.254.159.2558,190
11812.254.160.0/1912.254.160.1 to 12.254.191.25412.254.191.2558,190
11912.254.192.0/1912.254.192.1 to 12.254.223.25412.254.223.2558,190
12012.254.224.0/1912.254.224.1 to 12.254.255.25412.254.255.2558,190
12112.255.0.0/1912.255.0.1 to 12.255.31.25412.255.31.2558,190
12212.255.32.0/1912.255.32.1 to 12.255.63.25412.255.63.2558,190
12312.255.64.0/1912.255.64.1 to 12.255.95.25412.255.95.2558,190
12412.255.96.0/1912.255.96.1 to 12.255.127.25412.255.127.2558,190
12512.255.128.0/1912.255.128.1 to 12.255.159.25412.255.159.2558,190
12612.255.160.0/1912.255.160.1 to 12.255.191.25412.255.191.2558,190
12712.255.192.0/1912.255.192.1 to 12.255.223.25412.255.223.2558,190
12812.255.224.0/1912.255.224.1 to 12.255.255.25412.255.255.2558,190

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.