Count cells in a range from all worksheets using VBA in Microsoft Excel

It's possible to achieve this with the built-in COUNT() or COUNTA() function,
but that can be a big task if the workbook contains many worksheets,or if you frequently add new worksheets to the workbook.
To count a range from several worksheets you can use the COUNTA-function like this:

=COUNTA(Sheet1:Sheet10!A1:A100)

The formula above will count all non-blank cells in the range A1:A100 in the worksheets Sheet1 to Sheet10.
With the custom function below it's easy to count cells in a range from all the worksheets in a workbook:

Function CountAllWorksheets(InputRange As Range, InclAWS As Boolean) As Double
' counts the content of InputRange in all worksheets in the workbook
Dim ws As Worksheet, TempCount As Long
    Application.Volatile True ' calculates every time a cell changes
    TempCount = 0
    For Each ws In ActiveWorkbook.Worksheets
        If InclAWS Then ' include the active worksheet
            TempCount = TempCount + _
                Application.WorksheetFunction.Count(ws.Range(InputRange.Address))
        Else ' exclude the active worksheet
            If ws.Name <> ActiveSheet.Name Then ' not the active worksheet
                TempCount = TempCount + _
                    Application.WorksheetFunction.Count(ws.Range(InputRange.Address))
            End If
        End If
    Next ws
    Set ws = Nothing
    CountAllWorksheets = TempCount
End Function

This function is used in the same way as built-in worksheetfunctions.
In Excel 5/95 the variable InputRange must be defined as Variant instead of Range.
This function can easily be adapted for use with other worksheetfunctions that you wish
to use on all the worksheets in a workbook.