You can use
=IF(A1="","",IF(ISNA(VLOOKUP(A1,Sheet2!$A$2:$B$11,2,0)),"Incorrect Value
Entered",VLOOKUP(A1,Sheet2!$A$2:$B$11,2,0)))
replace A1 with the cell where you input the size
or hard coded which means you don't need the table in Sheet2
=IF(A1="","",IF(ISNA(VLOOKUP(A1,{"A",3.38;"B",2.63;"C",2.33;"D",2.04;"E",1.56;"F",1.04;"G",0.65;"H",0.41;"I",0.41;"J",25},2,0)),"Incorrect
Value
Entered",VLOOKUP(A1,{"A",3.38;"B",2.63;"C",2.33;"D",2.04;"E",1.56;"F",1.04;"G",0.65;"H",0.41;"I",0.41;"J",25},2,0)))
replace A1 with the cell where you input the size
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Regards,
Peo Sjoblom