Not Able to Get LOOKUP to Return Correct Data

I'm creating a spreadsheet for a concrete formwork course, and in order to do it I need to have the user input which size of lumber they are using (2x4, 4x4, etc.)

The function I'm having trouble with is

=IF(B16="S4S",LOOKUP(A31,Tables!A27:A65,Tables!C27:C65),LOOKUP(A31,Tables!A27:A65,Tables!B27:B65))

I want the user to be able to type in the size of the lumber, and whether its "Rough" or "S4S" and then have the spread sheet look up certain values like Area, Section Modulus, etc.

However, whenever I try it, the function doesn't always return the right values for the lumber. For instance, I'll put in 2x4 for input cell, but it'll put out values for a 2x12.

Sorry this is hard to explain, but I've attached the spreadsheet. The problem is under the 'Slab Form' tab. You input the lumber size in B13, and B31 is where the function is, and it should look up the values under the 'Tables' tab, under 'Board Properties.'

I'd appreciate any help you can offer

Thanks!

Try

=IF(B16="S4S", VLOOKUP(A31, Tables!A27:C65, 3, False), VLOOKUP(A31, Tables!A27:B65, 2, False))

Much better.

Not as short as darkyam's, but without IF

=INDEX(Tables!A26:C65,MATCH(A31,Tables!A26:A65,0),MATCH($B$16,Tables!A26:C26,0))