So what is the largest number in SharePoint numeric column?
Before we can answer this question, let take a look how SharePoint store the data in SQL table. By design, SharePoint will map specific column type in SharePoint into SQL data type; they are nvarchar, ntext, sqlvariant, int, float and bit. For example, true/false column will be mapped to bit and numeric column will be mapped to float.
There are two types of float data type in SQL, 7 digits or 15 digits precisions (http://msdn.