Every IPv4 prefix with its netmask, wildcard and host count, and the smaller tables you need for subnetting by hand. Select any row's prefix in the calculator to see the bits.
To size a subnet, find the first row whose usable hosts cover what you need: 50 hosts need a /26 (62 usable). To find the network an address belongs to, take the block size from the mask octet table and round the address down to a multiple of it: 192.168.1.77/27 has block size 32, and 77 rounds down to 64, so the network is 192.168.1.64/27. The subnetting tutorial explains each step, and the VLSM planner does it for a whole list of subnets.