Subnet Mask Information
courtesy of NetTects LLC

Netmask	Inverse	/CIDR	Usable	Size
0.0.0.0	255.255.255.255	/0	4,294,967,294	The Internet
128.0.0.0	127.255.255.255	/1	2,147,483,646	128 Class 'A's
192.0.0.0	63.255.255.255	/2	1,073,741,822	64 Class 'A's
224.0.0.0	31.255.255.255	/3	536,870,910	32 Class 'A's
240.0.0.0	15.255.255.255	/4	268,435,454	16 Class 'A's
248.0.0.0	7.255.255.255	/5	134,217,726	8 Class 'A's
252.0.0.0	3.255.255.255	/6	67,108,862	4 Class 'A's
254.0.0.0	1.255.255.255	/7	33,554,430	2 Class 'A's
255.0.0.0	0.255.255.255	/8	16,777,214	1 Class 'A'
255.128.0.0	0.127.255.255	/9	8,388,606	128 Class 'B's
255.192.0.0	0.63.255.255	/10	4,194,302	64 Class 'B's
255.224.0.0	0.31.255.255	/11	2,097,150	32 Class 'B's
255.240.0.0	0.15.255.255	/12	1,048,574	16 Class 'B's
255.248.0.0	0.7.255.255	/13	524,286	8 Class 'B's
255.252.0.0	0.3.255.255	/14	262,142	4 Class 'B's
255.254.0.0	0.1.255.255	/15	131,070	2 Class 'B's
255.255.0.0	0.0.255.255	/16	65,534	1 Class 'B'
255.255.128.0	0.0.127.255	/17	32,766	128 Class 'C's
255.255.192.0	0.0.63.255	/18	16,382	64 Class 'C's
255.255.224.0	0.0.31.255	/19	8,190	32 Class 'C's
255.255.240.0	0.0.15.255	/20	4,094	16 Class 'C's
255.255.248.0	0.0.7.255	/21	2,046	8 Class 'C's
255.255.252.0	0.0.3.255	/22	1,022	4 Class 'C's
255.255.254.0	0.0.1.255	/23	510	2 Class 'C's
255.255.255.0	0.0.0.255	/24	254	1 Class 'C'
255.255.255.128	0.0.0.127	/25	126	128 Hosts
255.255.255.192	0.0.0.63	/26	62	64 Hosts
255.255.255.224	0.0.0.31	/27	30	32 Hosts
255.255.255.240	0.0.0.15	/28	14	16 Hosts
255.255.255.248	0.0.0.7	/29	6	8 Hosts
255.255.255.252	0.0.0.3	/30	2	4 Hosts
255.255.255.254	0.0.0.1	/31	0	2 Hosts
255.255.255.255	0.0.0.0	/32	1	1 Host