The figure you calculate area in AutoCAD for goes straight into a quantity schedule, then a cost estimate, then a contract. One wrong number spoils the whole chain, and the software never tells you it just went wrong.
This article gathers the four ways to get an area, says which suits which moment, then spends most of its length on two silent traps that guides rarely mention. For the full drafting and quantity workflow, see the AutoCAD for Construction course.
The area command in AutoCAD: the real prompts and three options
The Autodesk AREA page describes it in one line: "Calculates the area and perimeter of objects or of defined areas". Note the words and perimeter — the command returns two numbers, not one.
Type AA and Enter. Here is the prompt on AutoCAD 2027, copied from the screen.
Specify first corner point or [Object/Add area/Subtract area] <Object>:
Those three options do three different jobs:
- Object is what you use nine times out of ten. Click a closed shape and both figures print.
- Add area turns on add mode. Pick the first shape, then the second, and a running total builds up.
- Subtract area takes away. This is how you measure a floor with a stairwell: add the slab, subtract the opening.
No prompt asks for a quantity, and none lets you window-select several shapes at once. The command takes one object at a time.
Area = 31415.9265, Circumference = 628.3185
That is the real result of measuring a circle of radius 100 at the Institute. Check it by hand: π times 100 squared is exactly 31415.9265.
Calculate perimeter in AutoCAD: one command, but the label changes
Beginners often think the software failed when no Perimeter label appears. In fact it is only naming the geometry correctly.
That label earns its keep: it tells you whether the shape is closed without opening the Properties palette to read the Closed row. It is also the key to the trap below.
An unclosed outline: the silent trap that costs the most
This is the part worth reading twice. Autodesk states it outright on the command page:
"If you select an open polyline, the area is calculated as if a line were drawn from the last point entered to the first. When the perimeter is calculated that line length is ignored."
In other words, on an open outline the area comes out as though the shape were closed, while the perimeter ignores the very edge that is missing. Two numbers describing two different shapes, with no warning of any kind.
We drew an L-shaped outline 400 wide and 400 high with a 200 by 200 corner cut away, then measured it on AutoCAD 2027. While the outline was still open:
Area = 120000.0000, Length = 1200.0000
Closing that same outline and measuring again:
Area = 120000.0000, Perimeter = 1600.0000
The area does not change by a single digit. The perimeter is short by 400, exactly the missing edge. And the label switched from Length to Perimeter. On a real plan, where the two ends sit a few thousandths of a unit apart, the eye cannot see it and neither can the print, but the schedule is wrong.
Measure area in AutoCAD when the shape is drawn from loose lines
A real floor plan rarely comes with a ready-made closed outline. Walls are separate LINE objects, and AREA will not join them for you.
You cannot calculate area in AutoCAD straight from loose lines, so one of two routes has to come first, and the BOUNDARY page covers the faster one:
PEDITwithMultipleand thenJointurns a set of loose segments into one polyline. This edits the original lines, which suits you when the outline is worth keeping.BOUNDARY, aliasedBOtouches nothing. It looks at the lines around the point you click and builds an extra polyline around that region. Delete it after measuring if you like.
Autodesk points to this route from the AREA page itself: "You can also use BOUNDARY to create a closed polyline or region and then use LIST or the Properties palette to find the area".
One habit worth forming: put those outlines on a layer of their own and turn off that layer's plot column. The issued drawing looks untouched, and you keep the outlines for a later check.
Hatch area in AutoCAD: the figure to trust
A hatch is not only there to be looked at. Select one, open the Properties palette with Ctrl and 1, and the Area box is right there — with the islands already deducted, so columns, walls and service ducts inside it are already out of the figure.
That makes it a better floor figure than measuring an outline and subtracting by hand. How to place a hatch and what its options do is covered in the HATCH command in CAD.
One thing we measured that several guides state backwards: AREA does accept a hatch. Selecting a 150 by 200 hatch with the Object option returns:
Area = 30000.0000, Perimeter = 700.0000
So a hatch yields a perimeter too, even though its Properties palette has no perimeter row at all.
Cumulative area in AutoCAD: why you rarely need a lisp file
Here is the real reason people go hunting for a lisp routine. Select every hatch, open Properties, and the Area box reads *VARIES* rather than a number. People conclude the software cannot add up, and go looking for a download.
Look at the row immediately below Area. It is called Cumulative Area, and it holds the sum already. We hatched three regions of 60000, 40000 and 30000 square units and selected all three: the palette read Hatch (3), the Area box read *VARIES*, and the Cumulative row read exactly 130000.
To grab every hatch in a drawing quickly, run QSELECT, set Object type to Hatch and accept. Three steps, no external file, and no unknown code running on your machine.
A lisp file still earns its place elsewhere: writing results into a table, labelling each room with its area, or repeating one job across hundreds of files. For a single total, the built-in tools already do it.
Units: where schedules usually go wrong
Every figure comes out in drawing units squared. Building plans are commonly drawn in millimetres, so one square metre is a million units. A room of 3200 by 2000 reads 6400000, and that is 6.4 square metres.
The cheapest check: calculate area in AutoCAD for one room whose size you already know, before building the whole schedule. An error of one decimal place shows up at once.
The final cross-check is worth doing every time as well: the room areas plus the wall area should equal the gross area. More than a couple of per cent out means a room was missed, or two outlines overlap.
Three things often repeated that are not true
| What you often hear | What AutoCAD 2027 actually does |
|---|---|
AutoCAD has three area commands: AA, LI and SS | Typing SS returns Unknown command. SS is the name of a third-party lisp file, not a command |
Type PE to get a perimeter | PE runs PEDIT, whose prompt is Select polyline or [Multiple]:. It edits polylines and prints no figure at all |
PERIMETER is a command | Typing it returns PERIMETER = 0.0000 (read only). It is a read-only variable holding the last perimeter computed, not a command |
The AREA and PERIMETER variables are handy: after a measurement, type the variable name to read the figure again without measuring twice. For more on typing commands and aliases, see drawing parallel lines in CAD.
Frequently asked questions
What is the alias for the area command in AutoCAD?
AA for AREA and LI for LIST. MEASUREGEOM, aliased MEA, also has an Area mode and shows the result right at the cursor.
Why is the area right but the perimeter wrong?
Your outline is not closed. The software closes the missing edge to compute an area but ignores that same edge for the perimeter. Read the label: Length instead of Perimeter gives it away.
How do I measure a region formed by several crossing lines?
Run BOUNDARY and click a point inside it. The software builds a closed outline, which you measure and then delete if you do not need it.
How do I measure a shape with curved edges?
Use MEASUREGEOM in Area mode and press A while tracing to switch to arc segments. You can trace a boundary mixing straight and curved parts without drawing an outline first.
Does a wide polyline measure along its edge or its centre?
Its centre. Autodesk states that "The centerline of a wide polyline is used to make area and perimeter calculations", so a duct drawn as a wide polyline gives the area of its centreline, not of its outer edge.
Do I need a lisp file to total several hatch areas?
No. Select all the hatches and read the Cumulative Area row in Properties. The Area box reading *VARIES* is normal, so do not stop there.