My students always have a hard time with converting from one measurement system to another or even within the same system!
I give this to all my incoming physics and physical science students on day one. It lists most of the common standard to metric equivalents needed in science. It also contains a few metric to metric just in case. The second page allows them to list the specific units and another column to list example formula that result in that unit as well.
If you want other units added just ask and I'll gladly add them!