Subnet cheat sheet

Every CIDR prefix from /0 to /32 mapped to its subnet mask, wildcard mask, usable hosts and total addresses — generated from our verified engine, so it’s exact (including the /31 and /32 special cases).

CIDR	Subnet mask	Wildcard	Usable hosts	Total addresses
/0	0.0.0.0	255.255.255.255	4,294,967,294	4,294,967,296
/1	128.0.0.0	127.255.255.255	2,147,483,646	2,147,483,648
/2	192.0.0.0	63.255.255.255	1,073,741,822	1,073,741,824
/3	224.0.0.0	31.255.255.255	536,870,910	536,870,912
/4	240.0.0.0	15.255.255.255	268,435,454	268,435,456
/5	248.0.0.0	7.255.255.255	134,217,726	134,217,728
/6	252.0.0.0	3.255.255.255	67,108,862	67,108,864
/7	254.0.0.0	1.255.255.255	33,554,430	33,554,432
/8	255.0.0.0	0.255.255.255	16,777,214	16,777,216
/9	255.128.0.0	0.127.255.255	8,388,606	8,388,608
/10	255.192.0.0	0.63.255.255	4,194,302	4,194,304
/11	255.224.0.0	0.31.255.255	2,097,150	2,097,152
/12	255.240.0.0	0.15.255.255	1,048,574	1,048,576
/13	255.248.0.0	0.7.255.255	524,286	524,288
/14	255.252.0.0	0.3.255.255	262,142	262,144
/15	255.254.0.0	0.1.255.255	131,070	131,072
/16	255.255.0.0	0.0.255.255	65,534	65,536
/17	255.255.128.0	0.0.127.255	32,766	32,768
/18	255.255.192.0	0.0.63.255	16,382	16,384
/19	255.255.224.0	0.0.31.255	8,190	8,192
/20	255.255.240.0	0.0.15.255	4,094	4,096
/21	255.255.248.0	0.0.7.255	2,046	2,048
/22	255.255.252.0	0.0.3.255	1,022	1,024
/23	255.255.254.0	0.0.1.255	510	512
/24	255.255.255.0	0.0.0.255	254	256
/25	255.255.255.128	0.0.0.127	126	128
/26	255.255.255.192	0.0.0.63	62	64
/27	255.255.255.224	0.0.0.31	30	32
/28	255.255.255.240	0.0.0.15	14	16
/29	255.255.255.248	0.0.0.7	6	8
/30	255.255.255.252	0.0.0.3	2	4
/31	255.255.255.254	0.0.0.1	2	2
/32	255.255.255.255	0.0.0.0	1	1

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CIDR & masks — common questions

How do I convert a CIDR prefix to a subnet mask?

The prefix is the number of leading 1-bits in the mask. /24 = 24 ones = 255.255.255.0; /26 = 255.255.255.192; /30 = 255.255.255.252. The table on this page lists every prefix from /0 to /32 with its mask, wildcard, usable hosts and total addresses — or use the live subnet calculator to convert a specific address.

Why does /31 show 2 usable hosts and /32 show 1?

A /31 is reserved for point-to-point links (RFC 3021), where both of the two addresses are usable — there is no network or broadcast address to subtract. A /32 is a single-host route (one address). Every other prefix subtracts the network and broadcast addresses, so usable = total − 2.

What is the wildcard mask used for?

The wildcard mask is the inverse of the subnet mask and is used in Cisco ACLs and OSPF to match address ranges. /24 has wildcard 0.0.0.255. The table includes the wildcard for every prefix.