Altium PCB dimensions
I do not think so, because the documentation does not list any special string with that content.

.Application_BuildNumber - the version of Altium Designer that the PCB is currently loaded in. When generating Gerber output, this string will record the software build that the design was created on
.Arc_Count - the number of arcs on the PCB
.Comment - the comment string for a component (used in designing component footprints)
.Component_Count - the number of components on the PCB
.ComputerName - The name of the machine that the PCB is currently loaded in
.Designator - the designator string for a component (used in designing component footprints)
.Fill_Count - the number of fills on the PCB
.Hole_Count - the number of drill holes on the PCB
.Layer_Name - the name of the layer the string is placed on
.Legend - a symbol legend for mechanical drill plots. This string is only valid when placed on the Drill Drawing layer
.Net_Count - the total number of different nets on the PCB
.Net_Names_On_Layer - the names of all nets on the specific layer. This string is only valid when placed on an internal plane layer
.Pad_Count - the number of pads on the PCB
.Pattern - the names of the component footprints used on the PCB
.Pcb_File_Name - the path and file name of the PCB document
.Pcb_File_Name_No_Path - the file name of the PCB document
.Plot_File_Name - When generating Gerber output, this string identifies the file name of the Gerber plot file. When generating printed output, this string identifies the layer depicted within the output. When generating ODB++ output, this string identifies the name of the parent folder in which the files are stored
.Poly_Count - the number of polygons on the PCB (consisting of polygon pours, internal planes and split planes)
.Print_Date - the date of printing/plotting
.Print_Scale - the printing/plot scale factor
.Print_Time - the time of printing/plotting
.Printout_Name - the name of the printout
.SlotHole_Count - the number of slotted holes on the PCB
.SquareHole_Count - the number of square holes on the PCB
.String_Count - the number of strings on the PCB
.Track_Count - the number of tracks on the PCB
.VersionControl_RevNumber - the current revision number of the document. Version control must be used for this string to contain any information
.Via_Count - the number of vias on the PCB.


Or am I missing your point?