Sharepoint Calculated Column

petertheo89 Try using below formula:

=IF(OR([Column A]="IA", [Column A]="IB", [Column A]="IIA"), 1, IF(OR([Column A]="IC", [Column A]="IIB", [Column A]="IIIA"), 2, IF(OR([Column A]="ID", [Column A]="IIC", [Column A]="IIIB", [Column A]="IVA"), 3, IF(OR([Column A]="IID", [Column A]="IIIC", [Column A]="IVB"), 4, IF(OR([Column A]="IIID", [Column A]="IVC"), 5, IF([Column A]="IVD", 6, 0))))))

Return the calculated field as Number.

Note:
Sometimes comma(,) does not work in formula (I am not sure but it is based on something language or regional settings on your site). So in that case use semicolon(;) instead of comma(,).

Official Documentations:

1. Calculated Field Formulas.
2. IF function.

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