CIDR Reference: /0 to /32

Every IPv4 CIDR prefix length, from /0 (the whole internet) to /32 (a single host). Each row shows the subnet mask, wildcard mask, total addresses, and usable hosts. Click any prefix for a full breakdown including cloud host counts for AWS, Azure, GCP, and OCI, or jump straight to the subnet calculator.

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

Usable hosts shown for standard mode (network + broadcast reserved). /31 is a 2-address point-to-point link (RFC 3021) and /32 is a single host. For cloud-specific counts, open any prefix page or the calculator.

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