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CIDR Cheat Sheet

This table lists every IPv4 CIDR prefix from /0 to /32 with the corresponding subnet mask, wildcard mask, address count, and usable host count. Click any prefix to see detailed examples and use cases.

CIDRSubnet MaskWildcard MaskTotal IPsUsable HostsNetwork BitsHost Bits
/32255.255.255.2550.0.0.011320
/31255.255.255.2540.0.0.122311
/30255.255.255.2520.0.0.342302
/29255.255.255.2480.0.0.786293
/28255.255.255.2400.0.0.151614284
/27255.255.255.2240.0.0.313230275
/26255.255.255.1920.0.0.636462266
/25255.255.255.1280.0.0.127128126257
/24255.255.255.00.0.0.255256254248
/23255.255.254.00.0.1.255512510239
/22255.255.252.00.0.3.2551,0241,0222210
/21255.255.248.00.0.7.2552,0482,0462111
/20255.255.240.00.0.15.2554,0964,0942012
/19255.255.224.00.0.31.2558,1928,1901913
/18255.255.192.00.0.63.25516,38416,3821814
/17255.255.128.00.0.127.25532,76832,7661715
/16255.255.0.00.0.255.25565,53665,5341616
/15255.254.0.00.1.255.255131,072131,0701517
/14255.252.0.00.3.255.255262,144262,1421418
/13255.248.0.00.7.255.255524,288524,2861319
/12255.240.0.00.15.255.2551,048,5761,048,5741220
/11255.224.0.00.31.255.2552,097,1522,097,1501121
/10255.192.0.00.63.255.2554,194,3044,194,3021022
/9255.128.0.00.127.255.2558,388,6088,388,606923
/8255.0.0.00.255.255.25516,777,21616,777,214824
/7254.0.0.01.255.255.25533,554,43233,554,430725
/6252.0.0.03.255.255.25567,108,86467,108,862626
/5248.0.0.07.255.255.255134,217,728134,217,726527
/4240.0.0.015.255.255.255268,435,456268,435,454428
/3224.0.0.031.255.255.255536,870,912536,870,910329
/2192.0.0.063.255.255.2551,073,741,8241,073,741,822230
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,646131
/00.0.0.0255.255.255.2554,294,967,2964,294,967,294032

Understanding CIDR Notation

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its associated network prefix. The number after the slash indicates how many of the 32 bits in an IPv4 address are dedicated to the network portion. A smaller prefix length like /8 means fewer network bits and more host bits, resulting in a larger network with more available addresses. A larger prefix like /28 allocates more bits to the network and fewer to hosts, creating a smaller subnet. This system replaced the older classful addressing scheme (Class A, B, C) and allows for far more flexible and efficient allocation of IP address space.

Common Subnet Sizes

  • /24 — 254 usable hosts. The standard subnet for most LANs and small office networks.
  • /16 — 65,534 usable hosts. Common for campus networks and large enterprise environments.
  • /30 — 2 usable hosts. Ideal for point-to-point links between routers.
  • /32 — Single host address. Used for loopback interfaces and host routes.

Private vs Public Subnets

RFC 1918 defines three IPv4 address ranges reserved for private use. These addresses are not routable on the public internet and can be freely used within internal networks:

  • 10.0.0.0/8 — 16,777,216 addresses (Class A private range)
  • 172.16.0.0/12 — 1,048,576 addresses (Class B private range)
  • 192.168.0.0/16 — 65,536 addresses (Class C private range)

Any address outside these ranges is considered public and must be assigned by a Regional Internet Registry (RIR). Most home and corporate networks use private addresses internally along with NAT (Network Address Translation) for internet access.

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