Use this command to take off each assembly you need to produce an estimate. It opens the Assembly Takeoff window where you choose an assembly and specify the takeoff quantities for its items. You also use the Assembly Takeoff window to review and change passes after an assembly has been generated into the spreadsheet.
On the ribbon, from the Takeoff group on the Takeoff tab, click Assembly.
Note: Assembly (Assembly Takeoff) is available only if you have an estimate open.