So, you need to work out the proportions of Doric or Ionic column and you left your reference books at home. They must be on the web, right? Yes they are, if you look in the right place.
The Institute of Classical Architecture & Art has a nice on-line reference of the five orders that’s very clear and easy to use. You can download each of the pages as a PDF, or just bookmark the site for easy reference. You can find it here.
Each of the drawings is accompanied by a brief but thorough explanation of the order and the proportions and nomenclature for each of the components.
Now you don’t need to panic if you can’t remember how to lay out the entasis on that column.