Subnet Calculator

Guide to IP allocations:

Mask         Slash  Usable IPs                Bitmap
---------------+--+-----------+-----------------------------------
0.0.0.0         /0  4294967294 00000000.00000000.00000000.00000000
128.0.0.0       /1  2147483646 10000000.00000000.00000000.00000000
192.0.0.0       /2  1073741822 11000000.00000000.00000000.00000000
224.0.0.0       /3   536870910 11100000.00000000.00000000.00000000
240.0.0.0       /4   268435454 11110000.00000000.00000000.00000000
248.0.0.0       /5   134217726 11111000.00000000.00000000.00000000
252.0.0.0       /6    67108862 11111100.00000000.00000000.00000000
254.0.0.0       /7    33554430 11111110.00000000.00000000.00000000
255.0.0.0       /8    16777214 11111111.00000000.00000000.00000000
255.128.0.0     /9     8388606 11111111.10000000.00000000.00000000
255.192.0.0     /10    4194302 11111111.11000000.00000000.00000000
255.224.0.0     /11    2097150 11111111.11100000.00000000.00000000
255.240.0.0     /12    1048574 11111111.11110000.00000000.00000000
255.248.0.0     /13     524286 11111111.11111000.00000000.00000000
255.252.0.0     /14     262142 11111111.11111100.00000000.00000000
255.254.0.0     /15     131070 11111111.11111110.00000000.00000000
255.255.0.0     /16      65534 11111111.11111111.00000000.00000000
255.255.128.0   /17      32766 11111111.11111111.10000000.00000000
255.255.192.0   /18      16382 11111111.11111111.11000000.00000000
255.255.224.0   /19       8190 11111111.11111111.11100000.00000000
255.255.240.0   /20       4094 11111111.11111111.11110000.00000000
255.255.248.0   /21       2046 11111111.11111111.11111000.00000000
255.255.252.0   /22       1022 11111111.11111111.11111100.00000000
255.255.254.0   /23        510 11111111.11111111.11111110.00000000
255.255.255.0   /24        254 11111111.11111111.11111111.00000000
255.255.255.128 /25        126 11111111.11111111.11111111.10000000
255.255.255.192 /26         62 11111111.11111111.11111111.11000000
255.255.255.224 /27         30 11111111.11111111.11111111.11100000
255.255.255.240 /28         14 11111111.11111111.11111111.11110000
255.255.255.248 /29          6 11111111.11111111.11111111.11111000
255.255.255.252 /30          2 11111111.11111111.11111111.11111100
255.255.255.254 /31          0 11111111.11111111.11111111.11111110

The slash notation is just the count of '1' bits in the mask.
W:15471 H:10938