There are several helpful bits of code for this.
Place your cursor in a merged cell and ask these questions in the Immidiate Window:
Is the activecell a merged cell?
? Activecell.Mergecells
True
How many cells are merged?
? Activecell.MergeArea.Cells.Count
2
How many columns are merged?
? Activecell.MergeArea.Columns.Count
2
How many rows are merged?
? Activecell.MergeArea.Rows.Count
1
What's the merged range address?
? activecell.MergeArea.Address
$F$2:$F$3