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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.

Network240.2.0.0/15
Usable hosts131,070
Subnet mask255.254.0.0
Addresses131,072
Network address
240.2.0.0
Broadcast address
240.3.255.255
First usable
240.2.0.1
Last usable
240.3.255.254
Usable hosts
131,070 (131,072 less the network and broadcast addresses)
Subnet mask
255.254.0.0
Wildcard mask
0.1.255.255 (Cisco ACLs, OSPF)
Prefix length
/15
Type
Reserved 240.0.0.0/4
Future use; not usable on most systems
Old class
E (reserved)
As numbers
Hex F0020000 · Integer 4026662912 to 4026793983
Reverse DNS zones
2.240.in-addr.arpa
3.240.in-addr.arpa
/15 is not on a 8-bit boundary, so it takes 2 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11110000.00000010.00000000.00000000240.2.0.0
Subnet mask11111111.11111110.00000000.00000000255.254.0.0
Network11110000.00000010.00000000.00000000240.2.0.0
Broadcast11110000.00000011.11111111.11111111240.3.255.255
Split into smaller subnets/21
/16 (2)/17 (4)/18 (8)/19 (16)/20 (32)/21 (64)/22 (128)/23 (256)/24 (512)/25 (1,024)/26 (2,048)/27 (4,096)

240.2.0.0/15 makes 64 subnets of /21.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1240.2.0.0/21240.2.0.1 to 240.2.7.254240.2.7.2552,046
2240.2.8.0/21240.2.8.1 to 240.2.15.254240.2.15.2552,046
3240.2.16.0/21240.2.16.1 to 240.2.23.254240.2.23.2552,046
4240.2.24.0/21240.2.24.1 to 240.2.31.254240.2.31.2552,046
5240.2.32.0/21240.2.32.1 to 240.2.39.254240.2.39.2552,046
6240.2.40.0/21240.2.40.1 to 240.2.47.254240.2.47.2552,046
7240.2.48.0/21240.2.48.1 to 240.2.55.254240.2.55.2552,046
8240.2.56.0/21240.2.56.1 to 240.2.63.254240.2.63.2552,046
9240.2.64.0/21240.2.64.1 to 240.2.71.254240.2.71.2552,046
10240.2.72.0/21240.2.72.1 to 240.2.79.254240.2.79.2552,046
11240.2.80.0/21240.2.80.1 to 240.2.87.254240.2.87.2552,046
12240.2.88.0/21240.2.88.1 to 240.2.95.254240.2.95.2552,046
13240.2.96.0/21240.2.96.1 to 240.2.103.254240.2.103.2552,046
14240.2.104.0/21240.2.104.1 to 240.2.111.254240.2.111.2552,046
15240.2.112.0/21240.2.112.1 to 240.2.119.254240.2.119.2552,046
16240.2.120.0/21240.2.120.1 to 240.2.127.254240.2.127.2552,046
17240.2.128.0/21240.2.128.1 to 240.2.135.254240.2.135.2552,046
18240.2.136.0/21240.2.136.1 to 240.2.143.254240.2.143.2552,046
19240.2.144.0/21240.2.144.1 to 240.2.151.254240.2.151.2552,046
20240.2.152.0/21240.2.152.1 to 240.2.159.254240.2.159.2552,046
21240.2.160.0/21240.2.160.1 to 240.2.167.254240.2.167.2552,046
22240.2.168.0/21240.2.168.1 to 240.2.175.254240.2.175.2552,046
23240.2.176.0/21240.2.176.1 to 240.2.183.254240.2.183.2552,046
24240.2.184.0/21240.2.184.1 to 240.2.191.254240.2.191.2552,046
25240.2.192.0/21240.2.192.1 to 240.2.199.254240.2.199.2552,046
26240.2.200.0/21240.2.200.1 to 240.2.207.254240.2.207.2552,046
27240.2.208.0/21240.2.208.1 to 240.2.215.254240.2.215.2552,046
28240.2.216.0/21240.2.216.1 to 240.2.223.254240.2.223.2552,046
29240.2.224.0/21240.2.224.1 to 240.2.231.254240.2.231.2552,046
30240.2.232.0/21240.2.232.1 to 240.2.239.254240.2.239.2552,046
31240.2.240.0/21240.2.240.1 to 240.2.247.254240.2.247.2552,046
32240.2.248.0/21240.2.248.1 to 240.2.255.254240.2.255.2552,046
33240.3.0.0/21240.3.0.1 to 240.3.7.254240.3.7.2552,046
34240.3.8.0/21240.3.8.1 to 240.3.15.254240.3.15.2552,046
35240.3.16.0/21240.3.16.1 to 240.3.23.254240.3.23.2552,046
36240.3.24.0/21240.3.24.1 to 240.3.31.254240.3.31.2552,046
37240.3.32.0/21240.3.32.1 to 240.3.39.254240.3.39.2552,046
38240.3.40.0/21240.3.40.1 to 240.3.47.254240.3.47.2552,046
39240.3.48.0/21240.3.48.1 to 240.3.55.254240.3.55.2552,046
40240.3.56.0/21240.3.56.1 to 240.3.63.254240.3.63.2552,046
41240.3.64.0/21240.3.64.1 to 240.3.71.254240.3.71.2552,046
42240.3.72.0/21240.3.72.1 to 240.3.79.254240.3.79.2552,046
43240.3.80.0/21240.3.80.1 to 240.3.87.254240.3.87.2552,046
44240.3.88.0/21240.3.88.1 to 240.3.95.254240.3.95.2552,046
45240.3.96.0/21240.3.96.1 to 240.3.103.254240.3.103.2552,046
46240.3.104.0/21240.3.104.1 to 240.3.111.254240.3.111.2552,046
47240.3.112.0/21240.3.112.1 to 240.3.119.254240.3.119.2552,046
48240.3.120.0/21240.3.120.1 to 240.3.127.254240.3.127.2552,046
49240.3.128.0/21240.3.128.1 to 240.3.135.254240.3.135.2552,046
50240.3.136.0/21240.3.136.1 to 240.3.143.254240.3.143.2552,046
51240.3.144.0/21240.3.144.1 to 240.3.151.254240.3.151.2552,046
52240.3.152.0/21240.3.152.1 to 240.3.159.254240.3.159.2552,046
53240.3.160.0/21240.3.160.1 to 240.3.167.254240.3.167.2552,046
54240.3.168.0/21240.3.168.1 to 240.3.175.254240.3.175.2552,046
55240.3.176.0/21240.3.176.1 to 240.3.183.254240.3.183.2552,046
56240.3.184.0/21240.3.184.1 to 240.3.191.254240.3.191.2552,046
57240.3.192.0/21240.3.192.1 to 240.3.199.254240.3.199.2552,046
58240.3.200.0/21240.3.200.1 to 240.3.207.254240.3.207.2552,046
59240.3.208.0/21240.3.208.1 to 240.3.215.254240.3.215.2552,046
60240.3.216.0/21240.3.216.1 to 240.3.223.254240.3.223.2552,046
61240.3.224.0/21240.3.224.1 to 240.3.231.254240.3.231.2552,046
62240.3.232.0/21240.3.232.1 to 240.3.239.254240.3.239.2552,046
63240.3.240.0/21240.3.240.1 to 240.3.247.254240.3.247.2552,046
64240.3.248.0/21240.3.248.1 to 240.3.255.254240.3.255.2552,046

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.