I need help with Excel

If I enter on excel the data of the chart appearing in the link, how can I ask Excel to output the actual diameter and the actual thickness from 2 input parameters that are the nominal diameter and the schedule. You are right, the outside diameter between 2 schedules is the same, it's the inside diameter that decreases, but it does not matter in my case. What I'm trying to calculate does not matter either. And I do not have problems doing dropdown list.

Here is an example:

Let's say the user wants to use the sheet for a 1/8 schedule 40 pipe. I want him to select 1/8 in a dropdown list and schedule 40 in another list. From there, I want excel to use those two data and be able to go in the chart (for which the data is somewhere hidden in the sheet) and output 0.405 as actual diameter and 0.068 for the thickness. I have tried to go with IF functions (IF(DROPDOWNLIST1="1/8";0.405;IF(DROPDOWNLIST1="3/16";0.540; etc), but there are too many levels of imbrication and excel does not allow it. 

Is there a function that takes the input parameter and can convert it to a row number( ex: A), takes a second parameter and converts it to a column number (ex: 1) and outputs the value of the case A1?

 Drogar