column has been defined as a "Decimal" type, the max. length is 19 characters (with 15 decimal places).

Can I change the formatted character length of a column in a .dbf file in Libre Calc? I am editing shapefiles for input into a spatial database. Thanks for your suggestions.

That’s a limitation of fixed width numeric fields in the dBaseIII file format, the overall length can’t be longer than 19 characters, including the decimal separator and a minus sign. Also note that a “precision” of more than 14 decimal digits (not decimals) doesn’t make much sense as floating point precision is limited.

To change the length of a field of a loaded .dbf file you can change the column header, e.g. to FIELDNAME,N,19,12 to have more room for digits before the decimal separator, but you’ll also have to change the number format(s) applied to the column’s data, because during export the maximum of characters (-integer.fraction) encountered is taken for the field length and decimals. Best to reset to the General format.