If you are using full AutoCAD (not LT), follow these steps:

Method 1: Quick One-Time Load (Fastest)

Method 2: Permanent Load (Add to Startup Suite)

This Visual LISP function works on any curve and returns a real number.

Change precision by modifying the prec variable (line ~15):

(setq prec 3) ; 3 decimal places

Uncomment unit conversion lines (~lines 50-55) for specific units.

For professional work, you need more. Let me walk you through a more robust routine called AT (Add Total) that is popular among surveyors and architects.

This post shows a compact, reliable AutoLISP routine to calculate the total area of selected closed polylines and closed circle/ellipse-like objects in an AutoCAD drawing, plus instructions for loading and using it.

For calculating net floor area (Gross area minus cores and shafts). It sums "Addition" objects (green layer) and subtracts "Subtraction" objects (red layer).