Nested IF Function - Condition Is Based On Two Values Within A Cell

I am working on creating a simple Excel Database of an Engineering Tool Room Inventory for work. However I can not seem to get one particular 'NESTED IF Function' to do what I want it to do. (In advance warning, I may be going down the wrong route and might have used the wrong Formula in Excel but from my understanding the 'IF' function seemed the most plausible.

Issue: All I would like to do is for a NESTED IF Function to be able to say this:

1. When a user inputs data into one column, for example 'Column A', with the following data: 4" Square
2. Then the neighbouring column, for example 'Column B', would have a NESTED IF Function.
3. Which would output a logical response, "A, B, C, D, E, F etc...", depending on what is written in Column A.
If 'Column A' - 4" Square, Then 'Column B' - A
If 'Column A' - 5" Square, Then 'Column B' - B
& So on...
But the NESTED IF Function should only put a logical response if there is certain values within the cell, for example:
User types a value into 'Column A' which contain - 4 & S, Then 'Column B' - A
User types a value into 'Column B' which contain - 5 & S, Then 'Column B' - B
& So on...

Currently to do the above function, I have utilised the following Excel NESTED IF Function:

[Code] .....

& The following happens:
1. User inputs data into 'Column A'
2. The NESTED IF Function then provides an automatic response.
3. However it relies on the data being inputted without the ' " (Quotation Symbol)'
4. & With me defining the exact phrase that should be typed into the cell, for example, "4" Square"

Other: I have attached an example worksheet of the NESTED IF Function in practice, with two tables. One showing what is happening with the code above and one table showing what I would like to happen but with no function.

Example - IF Function.xlsx