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IPv4 CIDR Cheat Sheet

Every prefix from /0 to /32 with its subnet mask, wildcard mask, total addresses, and usable host count. Bookmark it, print it, or keep it open next time you're subnetting.

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CIDR to subnet mask table (/0–/32)

Usable hosts = 2^(32 − prefix) − 2, except /31 (point-to-point, RFC 3021) and /32 (host route).

CIDRSubnet maskWildcard maskTotal addressesUsable hosts
/00.0.0.0255.255.255.2554,294,967,2964,294,967,294
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,646
/2192.0.0.063.255.255.2551,073,741,8241,073,741,822
/3224.0.0.031.255.255.255536,870,912536,870,910
/4240.0.0.015.255.255.255268,435,456268,435,454
/5248.0.0.07.255.255.255134,217,728134,217,726
/6252.0.0.03.255.255.25567,108,86467,108,862
/7254.0.0.01.255.255.25533,554,43233,554,430
/8255.0.0.00.255.255.25516,777,21616,777,214
/9255.128.0.00.127.255.2558,388,6088,388,606
/10255.192.0.00.63.255.2554,194,3044,194,302
/11255.224.0.00.31.255.2552,097,1522,097,150
/12255.240.0.00.15.255.2551,048,5761,048,574
/13255.248.0.00.7.255.255524,288524,286
/14255.252.0.00.3.255.255262,144262,142
/15255.254.0.00.1.255.255131,072131,070
/16255.255.0.00.0.255.25565,53665,534
/17255.255.128.00.0.127.25532,76832,766
/18255.255.192.00.0.63.25516,38416,382
/19255.255.224.00.0.31.2558,1928,190
/20255.255.240.00.0.15.2554,0964,094
/21255.255.248.00.0.7.2552,0482,046
/22255.255.252.00.0.3.2551,0241,022
/23255.255.254.00.0.1.255512510
/24255.255.255.00.0.0.255256254
/25255.255.255.1280.0.0.127128126
/26255.255.255.1920.0.0.636462
/27255.255.255.2240.0.0.313230
/28255.255.255.2400.0.0.151614
/29255.255.255.2480.0.0.786
/30255.255.255.2520.0.0.342
/31255.255.255.2540.0.0.122 (RFC 3021)
/32255.255.255.2550.0.0.011 (host route)

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CIDR cheat sheet FAQ

What is a CIDR cheat sheet?

A CIDR cheat sheet is a quick-reference table that maps each CIDR prefix length (like /24) to its dotted-decimal subnet mask, wildcard mask, total number of addresses, and number of usable hosts. It saves you from calculating powers of two by hand.

What is the subnet mask for a /24, /26, or /30?

A /24 is 255.255.255.0 (254 usable hosts), a /26 is 255.255.255.192 (62 usable hosts), and a /30 is 255.255.255.252 (2 usable hosts). See the full table above for every prefix from /0 to /32.

How do you calculate usable hosts from a prefix?

Usable hosts = 2^(32 − prefix) − 2, because the network and broadcast addresses are reserved. The two exceptions are /31, which has 2 usable addresses for point-to-point links (RFC 3021), and /32, which is a single host route.

What is a wildcard mask?

A wildcard mask is the bitwise inverse of a subnet mask — where the subnet mask has 1s, the wildcard has 0s. For example, the /24 mask 255.255.255.0 has the wildcard 0.0.0.255. Wildcard masks are used in Cisco ACLs and OSPF network statements.

Is this CIDR reference free?

Yes, it is completely free. For subnet calculations, VLSM planning, DNS lookup, ping, and traceroute on the go, download the free Subnet Plus app for iPhone, iPad, and Mac.

How to use this CIDR cheat sheet

Find your prefix length in the first column to read across to its subnet mask, wildcard mask, total address count, and usable hosts. Going the other way — from a subnet mask back to a prefix — works too: scan the mask column for a value like 255.255.255.192 and read the prefix (/26). The subnet calculator and VLSM designer do this automatically for any network, and the IPv6 calculator covers IPv6 prefixes.

CIDR, subnet masks, and wildcards

CIDR (Classless Inter-Domain Routing) notation writes a network as an address plus a prefix length, like 192.168.1.0/24. The prefix is the number of leading 1-bits in the subnet mask, so /24 means 24 one-bits — 255.255.255.0. The wildcard mask is the inverse and is used in access-control lists and routing protocols. The Subnet Plus app brings all of this to iPhone, iPad, and Mac, and it's been trusted by network engineers since 2013.