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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.

Network37.158.0.0/15
Usable hosts131,070
Subnet mask255.254.0.0
Addresses131,072
Network address
37.158.0.0
Broadcast address
37.159.255.255
First usable
37.158.0.1
Last usable
37.159.255.254
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
Public public
Old class
A (default /8)
As numbers
Hex 259E0000 · Integer 631111680 to 631242751
Reverse DNS zones
158.37.in-addr.arpa
159.37.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
Address00100101.10011110.00000000.0000000037.158.0.0
Subnet mask11111111.11111110.00000000.00000000255.254.0.0
Network00100101.10011110.00000000.0000000037.158.0.0
Broadcast00100101.10011111.11111111.1111111137.159.255.255
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)

37.158.0.0/15 makes 64 subnets of /21.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
137.158.0.0/2137.158.0.1 to 37.158.7.25437.158.7.2552,046
237.158.8.0/2137.158.8.1 to 37.158.15.25437.158.15.2552,046
337.158.16.0/2137.158.16.1 to 37.158.23.25437.158.23.2552,046
437.158.24.0/2137.158.24.1 to 37.158.31.25437.158.31.2552,046
537.158.32.0/2137.158.32.1 to 37.158.39.25437.158.39.2552,046
637.158.40.0/2137.158.40.1 to 37.158.47.25437.158.47.2552,046
737.158.48.0/2137.158.48.1 to 37.158.55.25437.158.55.2552,046
837.158.56.0/2137.158.56.1 to 37.158.63.25437.158.63.2552,046
937.158.64.0/2137.158.64.1 to 37.158.71.25437.158.71.2552,046
1037.158.72.0/2137.158.72.1 to 37.158.79.25437.158.79.2552,046
1137.158.80.0/2137.158.80.1 to 37.158.87.25437.158.87.2552,046
1237.158.88.0/2137.158.88.1 to 37.158.95.25437.158.95.2552,046
1337.158.96.0/2137.158.96.1 to 37.158.103.25437.158.103.2552,046
1437.158.104.0/2137.158.104.1 to 37.158.111.25437.158.111.2552,046
1537.158.112.0/2137.158.112.1 to 37.158.119.25437.158.119.2552,046
1637.158.120.0/2137.158.120.1 to 37.158.127.25437.158.127.2552,046
1737.158.128.0/2137.158.128.1 to 37.158.135.25437.158.135.2552,046
1837.158.136.0/2137.158.136.1 to 37.158.143.25437.158.143.2552,046
1937.158.144.0/2137.158.144.1 to 37.158.151.25437.158.151.2552,046
2037.158.152.0/2137.158.152.1 to 37.158.159.25437.158.159.2552,046
2137.158.160.0/2137.158.160.1 to 37.158.167.25437.158.167.2552,046
2237.158.168.0/2137.158.168.1 to 37.158.175.25437.158.175.2552,046
2337.158.176.0/2137.158.176.1 to 37.158.183.25437.158.183.2552,046
2437.158.184.0/2137.158.184.1 to 37.158.191.25437.158.191.2552,046
2537.158.192.0/2137.158.192.1 to 37.158.199.25437.158.199.2552,046
2637.158.200.0/2137.158.200.1 to 37.158.207.25437.158.207.2552,046
2737.158.208.0/2137.158.208.1 to 37.158.215.25437.158.215.2552,046
2837.158.216.0/2137.158.216.1 to 37.158.223.25437.158.223.2552,046
2937.158.224.0/2137.158.224.1 to 37.158.231.25437.158.231.2552,046
3037.158.232.0/2137.158.232.1 to 37.158.239.25437.158.239.2552,046
3137.158.240.0/2137.158.240.1 to 37.158.247.25437.158.247.2552,046
3237.158.248.0/2137.158.248.1 to 37.158.255.25437.158.255.2552,046
3337.159.0.0/2137.159.0.1 to 37.159.7.25437.159.7.2552,046
3437.159.8.0/2137.159.8.1 to 37.159.15.25437.159.15.2552,046
3537.159.16.0/2137.159.16.1 to 37.159.23.25437.159.23.2552,046
3637.159.24.0/2137.159.24.1 to 37.159.31.25437.159.31.2552,046
3737.159.32.0/2137.159.32.1 to 37.159.39.25437.159.39.2552,046
3837.159.40.0/2137.159.40.1 to 37.159.47.25437.159.47.2552,046
3937.159.48.0/2137.159.48.1 to 37.159.55.25437.159.55.2552,046
4037.159.56.0/2137.159.56.1 to 37.159.63.25437.159.63.2552,046
4137.159.64.0/2137.159.64.1 to 37.159.71.25437.159.71.2552,046
4237.159.72.0/2137.159.72.1 to 37.159.79.25437.159.79.2552,046
4337.159.80.0/2137.159.80.1 to 37.159.87.25437.159.87.2552,046
4437.159.88.0/2137.159.88.1 to 37.159.95.25437.159.95.2552,046
4537.159.96.0/2137.159.96.1 to 37.159.103.25437.159.103.2552,046
4637.159.104.0/2137.159.104.1 to 37.159.111.25437.159.111.2552,046
4737.159.112.0/2137.159.112.1 to 37.159.119.25437.159.119.2552,046
4837.159.120.0/2137.159.120.1 to 37.159.127.25437.159.127.2552,046
4937.159.128.0/2137.159.128.1 to 37.159.135.25437.159.135.2552,046
5037.159.136.0/2137.159.136.1 to 37.159.143.25437.159.143.2552,046
5137.159.144.0/2137.159.144.1 to 37.159.151.25437.159.151.2552,046
5237.159.152.0/2137.159.152.1 to 37.159.159.25437.159.159.2552,046
5337.159.160.0/2137.159.160.1 to 37.159.167.25437.159.167.2552,046
5437.159.168.0/2137.159.168.1 to 37.159.175.25437.159.175.2552,046
5537.159.176.0/2137.159.176.1 to 37.159.183.25437.159.183.2552,046
5637.159.184.0/2137.159.184.1 to 37.159.191.25437.159.191.2552,046
5737.159.192.0/2137.159.192.1 to 37.159.199.25437.159.199.2552,046
5837.159.200.0/2137.159.200.1 to 37.159.207.25437.159.207.2552,046
5937.159.208.0/2137.159.208.1 to 37.159.215.25437.159.215.2552,046
6037.159.216.0/2137.159.216.1 to 37.159.223.25437.159.223.2552,046
6137.159.224.0/2137.159.224.1 to 37.159.231.25437.159.231.2552,046
6237.159.232.0/2137.159.232.1 to 37.159.239.25437.159.239.2552,046
6337.159.240.0/2137.159.240.1 to 37.159.247.25437.159.247.2552,046
6437.159.248.0/2137.159.248.1 to 37.159.255.25437.159.255.2552,046

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.