@COUNTBLANK

Kenneth Rothschild 

You have found one of the many, many reasons why using merged cells is a bad idea...

If I interpret your question correctly, you'd need a custom function. The following is based on an idea of Harlan Grove:

Function RealBlank(rng As Range) As Long
    Dim c As Range
    Dim skip As Range
    Application.Volatile
    For Each c In rng
        If skip Is Nothing Then
            If c.Value = "" Then
                RealBlank = RealBlank + 1
            End If
            If c.MergeCells Then
                Set skip = c.MergeArea
            End If
        ElseIf Intersect(c, skip) Is Nothing Then
            If c.Value = "" Then
                RealBlank = RealBlank + 1
            End If
            If c.MergeCells Then
                Set skip = Union(skip, c.MergeArea)
            End If
        End If
    Next c
End Function

Kenneth Rothschild 

It works for me.

A1 has a value. B1 and C1 are empty. A1:C1 are merged.

=COUNTBLANK(A1:C1)

Result is 2.