What ASC does
ASC is mainly for double-byte character set languages. It converts full-width characters to half-width versions, which can help normalize imported text before comparisons or downstream cleanup.
Practical examples
Convert full-width characters in a cell
=ASC(A2)
Use this when a source system stores letters or numbers in full-width form and you need a normalized result.
Normalize a typed string directly
=ASC("ＡＢＣ１２３")
This returns the half-width equivalent, which is useful when testing how ASC changes Japanese full-width characters.
Common mistakes and notes
ASC is relevant mainly for DBCS languages
If your workbook uses ordinary Latin text only, ASC may appear to do nothing because there are no full-width characters to convert.
Unchanged text is still a valid result
When the source text does not contain full-width letters or numbers, ASC returns the original text unchanged.