HOWTO: Calculate MD5 checksum in Windows (and other checksums, too)

On Linux that's trivial - there is the md5sum program.

Windows does not come with such a tool, but you can use md5deep package.

md5deep is a cross-platform set of programs to compute MD5, SHA-1, SHA-256 Tiger, or Whirlpool message digests on an arbitrary number of files. The programs run on Windows, Linux, Cygwin, *BSD, OS X, Solaris, and should run on most other platforms. md5deep is similar to the md5sum program found in the GNU Coreutils package (...)