Thanks to J. H. Wright for posting this:
package require tcom set excel [::tcom::ref createobject Excel.Application] $excel Visible 1 set workbooks [$excel Workbooks] set workbook [$workbooks Add] set worksheets [$workbook Worksheets] set worksheet [$worksheets Item [expr 1]] set cells [$worksheet Cells] for {set row 1} {$row<=10} {incr row} { foreach column {A B C D E F G H I J K L} { $cells Item $row $column $column$row } } puts [[[$worksheet UsedRange] Columns] Count] puts [[[$worksheet UsedRange] Rows] Count]
[Show a similar result expressed in terms of CurrentRegion [L1 ].]
See also the Wiki pages on "Excel" and "tcom".