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SUMAREA LISP: Live Net Area Field With Subtraction

SUMAREA creates a live field totalling the length or area of selected objects, with the option to subtract a second selection.

What SumField does

The subtraction is what makes this more than a running total. Select the outline of a room, then select the columns and voids inside it, and the field reports the net floor area. Edit any of the boundaries and the figure follows.

Four commands. SUMLENGTH and SUMAREA work in drawing units. SUMLENGTHMM converts millimetres to metres; SUMAREAMM converts square millimetres to square metres.

The two converting commands exist for a reason. Drawings are routinely modelled in millimetres while schedules are wanted in metres — and doing that conversion in your head, forty times, is where mistakes come from.

How to use it

  1. Load the routine with APPLOAD, or put it on your support file search path.
  2. Type SUMAREA, or SUMAREAMM for a metric conversion.
  3. Select the boundaries to add.
  4. Select anything to subtract — columns, voids, openings.
  5. Pick a point for new MText, click a table cell to fill it, or choose Object to write into existing text, an attribute or a multileader.

How it works

Where a block or multileader carries several attributes you are asked which one. Set the tag argument in a command definition to skip that prompt.

Making your own variants is a matter of copying a command definition at the foot of the file. The three arguments are the target attribute tag — nil to be asked — whether to offer a subtraction prompt, and the field formatting code. A square-metre command that always writes into a tag called AREA is one line.

Notes and limits

  • Open objects still have an area. AutoCAD treats an unclosed boundary as though a straight line joined its two ends, so a boundary that was never properly closed returns the area of that implied closure rather than an error. Worth checking before trusting a total.
  • Use the MM commands on millimetre drawings. That is what they are for.
  • Deleting a referenced object breaks the field, which shows ####.
  • Fields update on regeneration, governed by FIELDEVAL.

Download and details

NameSumField — a live field totalling length or area, with subtraction
DownloadSumField.lsp — 26.8 KB, plain AutoLISP source. Downloads directly; no zip to unpack.
TypeAutoCAD AutoLISP routine
CommandsSUMAREA, SUMAREAMM, SUMLENGTH, SUMLENGTHMM
Requiresthe ActiveX layer (loaded automatically by the routine with vl-load-com); nothing extra — the dialog is written to a temporary file at run time and deleted again, so there is no .dcl to install.
Source size26.8 KB, 639 lines
Error handlingYes — a *error* handler restores every system variable it changed, on cancel as well as on error.
UndoThe whole operation is wrapped in a single undo group, so one U reverses all of it.
CompatibilityAutoCAD (any release with AutoLISP), BricsCAD, ZWCAD, GstarCAD, ProgeCAD and other IntelliCAD-based platforms. AutoCAD LT needs a LISP enabler. No .NET, no ObjectARX, no installer.
AuthorYZ, August 2026
LicenceFree to use, supplied “as is” with no warranty.

References