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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.

Network20.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
20.0.0.0
Broadcast address
21.255.255.255
First usable
20.0.0.1
Last usable
21.255.255.254
Usable hosts
33,554,430 (33,554,432 less the network and broadcast addresses)
Subnet mask
254.0.0.0
Wildcard mask
1.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/7
Type
Public public
Old class
A (default /8)
As numbers
Hex 14000000 · Integer 335544320 to 369098751
Reverse DNS zones
20.in-addr.arpa
21.in-addr.arpa
/7 is not on a 8-bit boundary, so it takes 2 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00010100.00000000.00000000.0000000020.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network00010100.00000000.00000000.0000000020.0.0.0
Broadcast00010101.11111111.11111111.1111111121.255.255.255
Split into smaller subnets/13
/8 (2)/9 (4)/10 (8)/11 (16)/12 (32)/13 (64)/14 (128)/15 (256)/16 (512)/17 (1,024)/18 (2,048)/19 (4,096)

20.0.0.0/7 makes 64 subnets of /13.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
120.0.0.0/1320.0.0.1 to 20.7.255.25420.7.255.255524,286
220.8.0.0/1320.8.0.1 to 20.15.255.25420.15.255.255524,286
320.16.0.0/1320.16.0.1 to 20.23.255.25420.23.255.255524,286
420.24.0.0/1320.24.0.1 to 20.31.255.25420.31.255.255524,286
520.32.0.0/1320.32.0.1 to 20.39.255.25420.39.255.255524,286
620.40.0.0/1320.40.0.1 to 20.47.255.25420.47.255.255524,286
720.48.0.0/1320.48.0.1 to 20.55.255.25420.55.255.255524,286
820.56.0.0/1320.56.0.1 to 20.63.255.25420.63.255.255524,286
920.64.0.0/1320.64.0.1 to 20.71.255.25420.71.255.255524,286
1020.72.0.0/1320.72.0.1 to 20.79.255.25420.79.255.255524,286
1120.80.0.0/1320.80.0.1 to 20.87.255.25420.87.255.255524,286
1220.88.0.0/1320.88.0.1 to 20.95.255.25420.95.255.255524,286
1320.96.0.0/1320.96.0.1 to 20.103.255.25420.103.255.255524,286
1420.104.0.0/1320.104.0.1 to 20.111.255.25420.111.255.255524,286
1520.112.0.0/1320.112.0.1 to 20.119.255.25420.119.255.255524,286
1620.120.0.0/1320.120.0.1 to 20.127.255.25420.127.255.255524,286
1720.128.0.0/1320.128.0.1 to 20.135.255.25420.135.255.255524,286
1820.136.0.0/1320.136.0.1 to 20.143.255.25420.143.255.255524,286
1920.144.0.0/1320.144.0.1 to 20.151.255.25420.151.255.255524,286
2020.152.0.0/1320.152.0.1 to 20.159.255.25420.159.255.255524,286
2120.160.0.0/1320.160.0.1 to 20.167.255.25420.167.255.255524,286
2220.168.0.0/1320.168.0.1 to 20.175.255.25420.175.255.255524,286
2320.176.0.0/1320.176.0.1 to 20.183.255.25420.183.255.255524,286
2420.184.0.0/1320.184.0.1 to 20.191.255.25420.191.255.255524,286
2520.192.0.0/1320.192.0.1 to 20.199.255.25420.199.255.255524,286
2620.200.0.0/1320.200.0.1 to 20.207.255.25420.207.255.255524,286
2720.208.0.0/1320.208.0.1 to 20.215.255.25420.215.255.255524,286
2820.216.0.0/1320.216.0.1 to 20.223.255.25420.223.255.255524,286
2920.224.0.0/1320.224.0.1 to 20.231.255.25420.231.255.255524,286
3020.232.0.0/1320.232.0.1 to 20.239.255.25420.239.255.255524,286
3120.240.0.0/1320.240.0.1 to 20.247.255.25420.247.255.255524,286
3220.248.0.0/1320.248.0.1 to 20.255.255.25420.255.255.255524,286
3321.0.0.0/1321.0.0.1 to 21.7.255.25421.7.255.255524,286
3421.8.0.0/1321.8.0.1 to 21.15.255.25421.15.255.255524,286
3521.16.0.0/1321.16.0.1 to 21.23.255.25421.23.255.255524,286
3621.24.0.0/1321.24.0.1 to 21.31.255.25421.31.255.255524,286
3721.32.0.0/1321.32.0.1 to 21.39.255.25421.39.255.255524,286
3821.40.0.0/1321.40.0.1 to 21.47.255.25421.47.255.255524,286
3921.48.0.0/1321.48.0.1 to 21.55.255.25421.55.255.255524,286
4021.56.0.0/1321.56.0.1 to 21.63.255.25421.63.255.255524,286
4121.64.0.0/1321.64.0.1 to 21.71.255.25421.71.255.255524,286
4221.72.0.0/1321.72.0.1 to 21.79.255.25421.79.255.255524,286
4321.80.0.0/1321.80.0.1 to 21.87.255.25421.87.255.255524,286
4421.88.0.0/1321.88.0.1 to 21.95.255.25421.95.255.255524,286
4521.96.0.0/1321.96.0.1 to 21.103.255.25421.103.255.255524,286
4621.104.0.0/1321.104.0.1 to 21.111.255.25421.111.255.255524,286
4721.112.0.0/1321.112.0.1 to 21.119.255.25421.119.255.255524,286
4821.120.0.0/1321.120.0.1 to 21.127.255.25421.127.255.255524,286
4921.128.0.0/1321.128.0.1 to 21.135.255.25421.135.255.255524,286
5021.136.0.0/1321.136.0.1 to 21.143.255.25421.143.255.255524,286
5121.144.0.0/1321.144.0.1 to 21.151.255.25421.151.255.255524,286
5221.152.0.0/1321.152.0.1 to 21.159.255.25421.159.255.255524,286
5321.160.0.0/1321.160.0.1 to 21.167.255.25421.167.255.255524,286
5421.168.0.0/1321.168.0.1 to 21.175.255.25421.175.255.255524,286
5521.176.0.0/1321.176.0.1 to 21.183.255.25421.183.255.255524,286
5621.184.0.0/1321.184.0.1 to 21.191.255.25421.191.255.255524,286
5721.192.0.0/1321.192.0.1 to 21.199.255.25421.199.255.255524,286
5821.200.0.0/1321.200.0.1 to 21.207.255.25421.207.255.255524,286
5921.208.0.0/1321.208.0.1 to 21.215.255.25421.215.255.255524,286
6021.216.0.0/1321.216.0.1 to 21.223.255.25421.223.255.255524,286
6121.224.0.0/1321.224.0.1 to 21.231.255.25421.231.255.255524,286
6221.232.0.0/1321.232.0.1 to 21.239.255.25421.239.255.255524,286
6321.240.0.0/1321.240.0.1 to 21.247.255.25421.247.255.255524,286
6421.248.0.0/1321.248.0.1 to 21.255.255.25421.255.255.255524,286

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.