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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.

Network205.0.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
205.0.0.0
Broadcast address
205.63.255.255
First usable
205.0.0.1
Last usable
205.63.255.254
Usable hosts
4,194,302 (4,194,304 less the network and broadcast addresses)
Subnet mask
255.192.0.0
Wildcard mask
0.63.255.255 (Cisco ACLs, OSPF)
Prefix length
/10
Type
Public public
Old class
C (default /24)
As numbers
Hex CD000000 · Integer 3439329280 to 3443523583
Reverse DNS zones
0.205.in-addr.arpa
1.205.in-addr.arpa
2.205.in-addr.arpa
3.205.in-addr.arpa
4.205.in-addr.arpa
5.205.in-addr.arpa
6.205.in-addr.arpa
7.205.in-addr.arpa
8.205.in-addr.arpa
9.205.in-addr.arpa
10.205.in-addr.arpa
11.205.in-addr.arpa
12.205.in-addr.arpa
13.205.in-addr.arpa
14.205.in-addr.arpa
15.205.in-addr.arpa
and 48 more
/10 is not on a 8-bit boundary, so it takes 64 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11001101.00000000.00000000.00000000205.0.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network11001101.00000000.00000000.00000000205.0.0.0
Broadcast11001101.00111111.11111111.11111111205.63.255.255
Split into smaller subnets/16
/11 (2)/12 (4)/13 (8)/14 (16)/15 (32)/16 (64)/17 (128)/18 (256)/19 (512)/20 (1,024)/21 (2,048)/22 (4,096)

205.0.0.0/10 makes 64 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1205.0.0.0/16205.0.0.1 to 205.0.255.254205.0.255.25565,534
2205.1.0.0/16205.1.0.1 to 205.1.255.254205.1.255.25565,534
3205.2.0.0/16205.2.0.1 to 205.2.255.254205.2.255.25565,534
4205.3.0.0/16205.3.0.1 to 205.3.255.254205.3.255.25565,534
5205.4.0.0/16205.4.0.1 to 205.4.255.254205.4.255.25565,534
6205.5.0.0/16205.5.0.1 to 205.5.255.254205.5.255.25565,534
7205.6.0.0/16205.6.0.1 to 205.6.255.254205.6.255.25565,534
8205.7.0.0/16205.7.0.1 to 205.7.255.254205.7.255.25565,534
9205.8.0.0/16205.8.0.1 to 205.8.255.254205.8.255.25565,534
10205.9.0.0/16205.9.0.1 to 205.9.255.254205.9.255.25565,534
11205.10.0.0/16205.10.0.1 to 205.10.255.254205.10.255.25565,534
12205.11.0.0/16205.11.0.1 to 205.11.255.254205.11.255.25565,534
13205.12.0.0/16205.12.0.1 to 205.12.255.254205.12.255.25565,534
14205.13.0.0/16205.13.0.1 to 205.13.255.254205.13.255.25565,534
15205.14.0.0/16205.14.0.1 to 205.14.255.254205.14.255.25565,534
16205.15.0.0/16205.15.0.1 to 205.15.255.254205.15.255.25565,534
17205.16.0.0/16205.16.0.1 to 205.16.255.254205.16.255.25565,534
18205.17.0.0/16205.17.0.1 to 205.17.255.254205.17.255.25565,534
19205.18.0.0/16205.18.0.1 to 205.18.255.254205.18.255.25565,534
20205.19.0.0/16205.19.0.1 to 205.19.255.254205.19.255.25565,534
21205.20.0.0/16205.20.0.1 to 205.20.255.254205.20.255.25565,534
22205.21.0.0/16205.21.0.1 to 205.21.255.254205.21.255.25565,534
23205.22.0.0/16205.22.0.1 to 205.22.255.254205.22.255.25565,534
24205.23.0.0/16205.23.0.1 to 205.23.255.254205.23.255.25565,534
25205.24.0.0/16205.24.0.1 to 205.24.255.254205.24.255.25565,534
26205.25.0.0/16205.25.0.1 to 205.25.255.254205.25.255.25565,534
27205.26.0.0/16205.26.0.1 to 205.26.255.254205.26.255.25565,534
28205.27.0.0/16205.27.0.1 to 205.27.255.254205.27.255.25565,534
29205.28.0.0/16205.28.0.1 to 205.28.255.254205.28.255.25565,534
30205.29.0.0/16205.29.0.1 to 205.29.255.254205.29.255.25565,534
31205.30.0.0/16205.30.0.1 to 205.30.255.254205.30.255.25565,534
32205.31.0.0/16205.31.0.1 to 205.31.255.254205.31.255.25565,534
33205.32.0.0/16205.32.0.1 to 205.32.255.254205.32.255.25565,534
34205.33.0.0/16205.33.0.1 to 205.33.255.254205.33.255.25565,534
35205.34.0.0/16205.34.0.1 to 205.34.255.254205.34.255.25565,534
36205.35.0.0/16205.35.0.1 to 205.35.255.254205.35.255.25565,534
37205.36.0.0/16205.36.0.1 to 205.36.255.254205.36.255.25565,534
38205.37.0.0/16205.37.0.1 to 205.37.255.254205.37.255.25565,534
39205.38.0.0/16205.38.0.1 to 205.38.255.254205.38.255.25565,534
40205.39.0.0/16205.39.0.1 to 205.39.255.254205.39.255.25565,534
41205.40.0.0/16205.40.0.1 to 205.40.255.254205.40.255.25565,534
42205.41.0.0/16205.41.0.1 to 205.41.255.254205.41.255.25565,534
43205.42.0.0/16205.42.0.1 to 205.42.255.254205.42.255.25565,534
44205.43.0.0/16205.43.0.1 to 205.43.255.254205.43.255.25565,534
45205.44.0.0/16205.44.0.1 to 205.44.255.254205.44.255.25565,534
46205.45.0.0/16205.45.0.1 to 205.45.255.254205.45.255.25565,534
47205.46.0.0/16205.46.0.1 to 205.46.255.254205.46.255.25565,534
48205.47.0.0/16205.47.0.1 to 205.47.255.254205.47.255.25565,534
49205.48.0.0/16205.48.0.1 to 205.48.255.254205.48.255.25565,534
50205.49.0.0/16205.49.0.1 to 205.49.255.254205.49.255.25565,534
51205.50.0.0/16205.50.0.1 to 205.50.255.254205.50.255.25565,534
52205.51.0.0/16205.51.0.1 to 205.51.255.254205.51.255.25565,534
53205.52.0.0/16205.52.0.1 to 205.52.255.254205.52.255.25565,534
54205.53.0.0/16205.53.0.1 to 205.53.255.254205.53.255.25565,534
55205.54.0.0/16205.54.0.1 to 205.54.255.254205.54.255.25565,534
56205.55.0.0/16205.55.0.1 to 205.55.255.254205.55.255.25565,534
57205.56.0.0/16205.56.0.1 to 205.56.255.254205.56.255.25565,534
58205.57.0.0/16205.57.0.1 to 205.57.255.254205.57.255.25565,534
59205.58.0.0/16205.58.0.1 to 205.58.255.254205.58.255.25565,534
60205.59.0.0/16205.59.0.1 to 205.59.255.254205.59.255.25565,534
61205.60.0.0/16205.60.0.1 to 205.60.255.254205.60.255.25565,534
62205.61.0.0/16205.61.0.1 to 205.61.255.254205.61.255.25565,534
63205.62.0.0/16205.62.0.1 to 205.62.255.254205.62.255.25565,534
64205.63.0.0/16205.63.0.1 to 205.63.255.254205.63.255.25565,534

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.