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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.

Network51.0.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
51.0.0.0
Broadcast address
51.63.255.255
First usable
51.0.0.1
Last usable
51.63.255.254
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
A (default /8)
As numbers
Hex 33000000 · Integer 855638016 to 859832319
Reverse DNS zones
0.51.in-addr.arpa
1.51.in-addr.arpa
2.51.in-addr.arpa
3.51.in-addr.arpa
4.51.in-addr.arpa
5.51.in-addr.arpa
6.51.in-addr.arpa
7.51.in-addr.arpa
8.51.in-addr.arpa
9.51.in-addr.arpa
10.51.in-addr.arpa
11.51.in-addr.arpa
12.51.in-addr.arpa
13.51.in-addr.arpa
14.51.in-addr.arpa
15.51.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
Address00110011.00000000.00000000.0000000051.0.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network00110011.00000000.00000000.0000000051.0.0.0
Broadcast00110011.00111111.11111111.1111111151.63.255.255
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)

51.0.0.0/10 makes 64 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
151.0.0.0/1651.0.0.1 to 51.0.255.25451.0.255.25565,534
251.1.0.0/1651.1.0.1 to 51.1.255.25451.1.255.25565,534
351.2.0.0/1651.2.0.1 to 51.2.255.25451.2.255.25565,534
451.3.0.0/1651.3.0.1 to 51.3.255.25451.3.255.25565,534
551.4.0.0/1651.4.0.1 to 51.4.255.25451.4.255.25565,534
651.5.0.0/1651.5.0.1 to 51.5.255.25451.5.255.25565,534
751.6.0.0/1651.6.0.1 to 51.6.255.25451.6.255.25565,534
851.7.0.0/1651.7.0.1 to 51.7.255.25451.7.255.25565,534
951.8.0.0/1651.8.0.1 to 51.8.255.25451.8.255.25565,534
1051.9.0.0/1651.9.0.1 to 51.9.255.25451.9.255.25565,534
1151.10.0.0/1651.10.0.1 to 51.10.255.25451.10.255.25565,534
1251.11.0.0/1651.11.0.1 to 51.11.255.25451.11.255.25565,534
1351.12.0.0/1651.12.0.1 to 51.12.255.25451.12.255.25565,534
1451.13.0.0/1651.13.0.1 to 51.13.255.25451.13.255.25565,534
1551.14.0.0/1651.14.0.1 to 51.14.255.25451.14.255.25565,534
1651.15.0.0/1651.15.0.1 to 51.15.255.25451.15.255.25565,534
1751.16.0.0/1651.16.0.1 to 51.16.255.25451.16.255.25565,534
1851.17.0.0/1651.17.0.1 to 51.17.255.25451.17.255.25565,534
1951.18.0.0/1651.18.0.1 to 51.18.255.25451.18.255.25565,534
2051.19.0.0/1651.19.0.1 to 51.19.255.25451.19.255.25565,534
2151.20.0.0/1651.20.0.1 to 51.20.255.25451.20.255.25565,534
2251.21.0.0/1651.21.0.1 to 51.21.255.25451.21.255.25565,534
2351.22.0.0/1651.22.0.1 to 51.22.255.25451.22.255.25565,534
2451.23.0.0/1651.23.0.1 to 51.23.255.25451.23.255.25565,534
2551.24.0.0/1651.24.0.1 to 51.24.255.25451.24.255.25565,534
2651.25.0.0/1651.25.0.1 to 51.25.255.25451.25.255.25565,534
2751.26.0.0/1651.26.0.1 to 51.26.255.25451.26.255.25565,534
2851.27.0.0/1651.27.0.1 to 51.27.255.25451.27.255.25565,534
2951.28.0.0/1651.28.0.1 to 51.28.255.25451.28.255.25565,534
3051.29.0.0/1651.29.0.1 to 51.29.255.25451.29.255.25565,534
3151.30.0.0/1651.30.0.1 to 51.30.255.25451.30.255.25565,534
3251.31.0.0/1651.31.0.1 to 51.31.255.25451.31.255.25565,534
3351.32.0.0/1651.32.0.1 to 51.32.255.25451.32.255.25565,534
3451.33.0.0/1651.33.0.1 to 51.33.255.25451.33.255.25565,534
3551.34.0.0/1651.34.0.1 to 51.34.255.25451.34.255.25565,534
3651.35.0.0/1651.35.0.1 to 51.35.255.25451.35.255.25565,534
3751.36.0.0/1651.36.0.1 to 51.36.255.25451.36.255.25565,534
3851.37.0.0/1651.37.0.1 to 51.37.255.25451.37.255.25565,534
3951.38.0.0/1651.38.0.1 to 51.38.255.25451.38.255.25565,534
4051.39.0.0/1651.39.0.1 to 51.39.255.25451.39.255.25565,534
4151.40.0.0/1651.40.0.1 to 51.40.255.25451.40.255.25565,534
4251.41.0.0/1651.41.0.1 to 51.41.255.25451.41.255.25565,534
4351.42.0.0/1651.42.0.1 to 51.42.255.25451.42.255.25565,534
4451.43.0.0/1651.43.0.1 to 51.43.255.25451.43.255.25565,534
4551.44.0.0/1651.44.0.1 to 51.44.255.25451.44.255.25565,534
4651.45.0.0/1651.45.0.1 to 51.45.255.25451.45.255.25565,534
4751.46.0.0/1651.46.0.1 to 51.46.255.25451.46.255.25565,534
4851.47.0.0/1651.47.0.1 to 51.47.255.25451.47.255.25565,534
4951.48.0.0/1651.48.0.1 to 51.48.255.25451.48.255.25565,534
5051.49.0.0/1651.49.0.1 to 51.49.255.25451.49.255.25565,534
5151.50.0.0/1651.50.0.1 to 51.50.255.25451.50.255.25565,534
5251.51.0.0/1651.51.0.1 to 51.51.255.25451.51.255.25565,534
5351.52.0.0/1651.52.0.1 to 51.52.255.25451.52.255.25565,534
5451.53.0.0/1651.53.0.1 to 51.53.255.25451.53.255.25565,534
5551.54.0.0/1651.54.0.1 to 51.54.255.25451.54.255.25565,534
5651.55.0.0/1651.55.0.1 to 51.55.255.25451.55.255.25565,534
5751.56.0.0/1651.56.0.1 to 51.56.255.25451.56.255.25565,534
5851.57.0.0/1651.57.0.1 to 51.57.255.25451.57.255.25565,534
5951.58.0.0/1651.58.0.1 to 51.58.255.25451.58.255.25565,534
6051.59.0.0/1651.59.0.1 to 51.59.255.25451.59.255.25565,534
6151.60.0.0/1651.60.0.1 to 51.60.255.25451.60.255.25565,534
6251.61.0.0/1651.61.0.1 to 51.61.255.25451.61.255.25565,534
6351.62.0.0/1651.62.0.1 to 51.62.255.25451.62.255.25565,534
6451.63.0.0/1651.63.0.1 to 51.63.255.25451.63.255.25565,534

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.