Visual Basic para Aplicaciones - Contar celdas en excell

Dim oExcel As Object

Dim oBook As Object

Dim oSheet As Object

Dim fileName As String = "C:\prueba1.xlsx"

Dim total As Integer

If Not My.Computer.FileSystem.FileExists(fileName) Then

    MsgBox(fileName & " No existe")

    Exit Sub

End If

' Set the object variable to refer to the file you want to use.

oExcel = CreateObject("Excel.Application")

oBook = oExcel.Workbooks.Open(fileName, ReadOnly:=True)

oSheet = oExcel.Worksheets("Hoja1")

total = oExcel.WorksheetFunction.count(oSheet.Range("A1:A65536"))

' por si quieres sumarlos de la casilla A1 a la A3

'total = oExcel.WorksheetFunction.Sum(oSheet.Range("A1:A3")) 

MsgBox(total)