IPv4 Subnet Cheat Sheet

A complete reference table for IPv4 CIDR notation, subnet masks, wildcard masks, and host capacities. Click any prefix or mask to open it in the interactive calculator.

CIDR Prefix	Subnet Mask	Wildcard Mask	Total IPs	Usable Hosts	Notes
/0	0.0.0.0	255.255.255.255	4,294,967,296	0	Default Route
/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	Class A / Largest Private Block
/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	Private Block (172.16.0.0/12)
/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	Class B / Private Block
/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	Class C / Standard LAN
/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	Point-to-Point (RFC 3021)
/32	255.255.255.255	0.0.0.0	1	1	Single Host

How to use this subnet cheat sheet

This reference table provides an instant mapping between the three common ways network engineers represent IP subnets:

CIDR Prefix (/X): Used in modern routing tables, AWS/Azure VPC configurations, and Linux networking.
Subnet Mask: The traditional dotted-decimal format required by Windows networking and legacy firewalls.
Wildcard Mask: The inverse of the subnet mask, heavily used in Cisco IOS Access Control Lists (ACLs) and OSPF routing configurations.

Usable vs Total Hosts

In standard IPv4 subnets (from /1 to /30), two IP addresses are reserved and cannot be assigned to hosts. The first IP address is the Network Address (used to identify the subnet itself), and the last IP address is the Broadcast Address. This is why a /24 network has 256 total IPs but only 254 usable hosts.

The notable exceptions are /31 networks (used for point-to-point links per RFC 3021, providing exactly 2 usable IPs) and /32 networks (which represent a single host or loopback interface).