I just wrote a page on How to Safely Convert From One Unit to Another.
Please check it, because there is so much complicated formatting I may have made a silly mistake somewhere!
Suggestions welcome also.
"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman
Maybe you might wanna include that
ms-¹ × 3.6 = kmh-¹
kmh-¹ ÷ 3.6 = ms-¹