A drawing that has passed through several hands starts to feel heavy. You pick a wall line and delete it, and an identical line is sitting underneath. Total up the lengths and the figure comes out half again too large. Duplicate linework lies stacked where the eye cannot see it, and the software counts every layer of it.
Removing duplicate lines in AutoCAD is the job of OVERKILL, and it does the whole thing in one pass. This article sets out what it discards, what it keeps, and why it sometimes appears to do nothing at all. For the wider subject of drawing management, the Institute runs an AutoCAD course for construction.
What the OVERKILL command does
Autodesk describes it in one line on the OVERKILL page for the 2027 release: "Removes duplicate or overlapping lines, arcs, and polylines. Also, combines those that are partially overlapping or contiguous".
It does two different things, and telling them apart is what makes the command make sense.
Deleting duplicates. Two lines lying exactly on top of one another: one stays, one goes.
Merging contiguous segments. Two collinear lines end to end become a single longer line.
The second is what really tidies a drawing. A wall drawn as twelve separate pieces becomes one, easy to select, easy to offset, easy to measure.
Where to start it
Before removing duplicate lines in AutoCAD you have to find the command, and it sits somewhere unobvious.
| Command | Alias | Ribbon | Classic menu |
|---|---|---|---|
OVERKILL | none | Home → Modify | Modify → Delete Duplicate Objects |
PURGE | PU | none | File → Drawing Utilities → Purge |
AUDIT | none | none | File → Drawing Utilities → Audit |
There is no alias, so the whole word gets typed.
One point rarely mentioned: a hyphenated -OVERKILL exists and runs entirely on the command line, so it can go inside a script or a lisp routine. The ordinary command insists on its dialog.
Six lines in, three lines out
Take a drawing holding three typical cases side by side: three lines stacked exactly on top of one another, two collinear lines end to end, and one line that matches nothing. Six objects in total.
Run the command once across all six.
| Case | After the cleanup | Removed |
|---|---|---|
| 3 lines stacked exactly | 1 remains | 2 lines |
| 2 collinear lines end to end | merged into 1 | 1 line |
| 1 line matching nothing | untouched | nothing |
| Six objects in total | three remain | 3 lines |
The software reports exactly two figures.
2 duplicate(s) deleted
1 overlapping object(s) or segment(s) deleted
Those add up to the three lines that vanished, and they separate the two jobs: two removed as duplicates, one absorbed into its neighbour.
The third row is the reassuring one. A line that matches nothing is left alone. The command does not delete indiscriminately.
The opening figure is that same drawing, photographed after the cleanup. It looks no different from before, which is exactly why nobody notices a drawing carrying duplicate linework.
Step by step on the command line
| Step | What the machine asks | What you do |
|---|---|---|
| 1 | Command: | Type OVERKILL and press Enter |
| 2 | Select objects: | Select the area and press Enter |
| 3 | The Delete Duplicate Objects dialog appears | Check the settings and click OK |
With the hyphenated form, step three becomes two lines on the command line instead.
Current settings: Tolerance=0.000001, Ignore=None, Optimize polylines=Yes,
Combine partial overlap=Yes, Combine end-to-end=Yes
Enter an option to change
[Done/Ignore/tOlerance/optimize Plines/combine parTial overlap/combine Endtoend/Associativity] <done>:Pressing Enter runs it with the settings shown. That settings line repays reading, because two of the values in it decide whether the command does anything at all.
Why duplicate objects survive the cleanup
This is the commonest complaint, and there are two causes.
The first: different layers. By default Ignore=None, meaning no property is disregarded. Two lines lying exactly on top of each other but sitting on different layers count as two different objects, and both stay.
Place two such pairs side by side — one pair on different layers, one pair on the same layer — run the command, and the report reads 1 duplicate(s) deleted. The same-layer pair merged; the different-layer pair did not.
To merge across layers, choose Ignore at the prompt and set it to disregard the layer property. But think first: after merging, the surviving line sits on one layer only, and that may not be the layer you wanted.
The second: tolerance. The Tolerance setting defaults to 0.000001, which is very tight. Two lines a thousandth of a unit apart still count as different. On a drawing where snapping was casual, lines are nearly coincident rather than coincident. Raising the tolerance gathers them, but raise it too far and the command merges lines that were meant to stay separate.
The optimize Plines option works inside each polyline instead, discarding zero-length and overlapping segments. Zero-length segments are commoner than people expect: they appear whenever a vertex gets placed twice at the same point, which happens easily when snapping is on and the cursor barely moves. They are invisible, they add vertices to every polyline that carries them, and they make grip editing behave oddly because two grips sit at one location.
There is a third cause of apparent inaction worth naming. The command works only on what you selected. Selecting with a crossing window catches objects that merely touch the window edge, but a duplicate lying wholly outside it is never examined. On a large sheet, zoom out until the whole drawing is visible and draw the window right around it, so nothing sits outside the selection. Then read the report to see how much was found. Editing polylines is covered in our article on polylines in AutoCAD.
The three commands that belong together
OVERKILL only cleans geometry. Making a drawing genuinely lighter takes two more, and the order matters.
| Order | Command | What it clears |
|---|---|---|
| 1 | AUDIT | Structural errors inside the file |
| 2 | OVERKILL | Duplicate and contiguous linework |
| 3 | PURGE, aliased PU | Unused layers, text styles, blocks, linetypes |
Running OVERKILL before the PURGE command has a reason behind it: clearing the linework is what leaves layers with nothing on them, ready to be purged.
A note on safety. OVERKILL deletes for real and does not ask twice. Save a copy before running it on anything important, or at least remember that U still steps back — covered in our article on undo in AutoCAD.
Three things tutorials leave out
| What people assume | What the 2027 release actually does |
|---|---|
| It only deletes duplicates | It also merges contiguous lines, which is the part that tidies a drawing |
| Afterwards no duplicates remain | Lines on different layers survive, because Ignore=None by default |
| The dialog is the only way in | -OVERKILL runs on the command line and works inside a script |
Type OVERKILL, window the whole drawing, press Enter twice. The two reported figures say how much went; if they read zero, check layers and tolerance before concluding the drawing was clean.
A fair question follows: does removing duplicate lines in AutoCAD actually make a file meaningfully smaller? Honestly, it depends on the drawing. A carefully drafted set barely changes. A drawing that has been copied and pasted over itself repeatedly can shed a few per cent of its objects, and the real gain lies elsewhere anyway — picking the line you meant on the first click rather than the third.
There is a second habit worth pairing with it. Run the cleanup before issuing a drawing to anyone outside the office, not after receiving one. A recipient who runs it on your file and watches hundreds of objects disappear will draw conclusions about how the set was produced, and they will not be flattering ones. It costs a minute and it is the sort of thing that quietly shapes a reputation.
There is a further benefit that goes unnoticed. Duplicate linework corrupts every total you take off a drawing: pipe runs, wall perimeters, hatch areas. Quantities taken from an uncleaned drawing come out high, and nobody knows by how much until the duplicates are gone. Cleaning before measuring is a habit worth forming.
Frequently asked questions
What is the alias for OVERKILL?
There is none. Type it in full, or use the button at Home → Modify.
It ran but the duplicates are still there.
Check two things: whether the lines share a layer, and whether they really coincide. By default no property is disregarded and the tolerance is only 0.000001.
Could it delete something I still need?
No. A line matching nothing else is left untouched.
How do I know how much it removed?
Read the two lines it prints: duplicate(s) deleted for stacked copies, overlapping object(s) or segment(s) deleted for merges.
Which command should run first to lighten a drawing?
AUDIT, then OVERKILL, then PURGE. Clearing linework is what exposes the empty layers.
Can it be scripted?
Yes, using the hyphenated -OVERKILL.