The add-in Adequate contains a wizard that allows you to change from one function to another within certain categories.

First choose a category (Length, weight, temperature or time). Then pick the source unit, the target unit and the value of the source. These can be constants or references (relative or absolute) to cells. Now, the conversion will take place.

The Convert Wizard of HJGSoft Adequate add-in
The Convert Wizard of HJGSoft Adequate add-in
Example Convert-function
Example Convert-function