Every wall on a floor plan is two lines. The familiar approach is to draw one and OFFSET it, but that means two passes and two alignments for every wall. The mline command in AutoCAD draws both faces in one pass, and you type the thickness straight in.
This article measures each option on AutoCAD 2027 at the Institute using the object's own bounding box. For a full grounding in floor plans see our AutoCAD for Construction course.
Where to start it, and how well it is hidden
Read straight out of the acad.cuix interface file of the 2027 release on the machine, and the result explains why so few people know this family exists.
| Command | Alias | Ribbon | Classic menu |
|---|---|---|---|
MLINE | ML | none | Draw → Multiline |
MLSTYLE | none | none | Format → Multiline Style |
MLEDIT | none | none | Modify → Object → Multiline |
None of the three has a ribbon button, and none has a toolbar button either. AutoCAD's default interface today is the ribbon, so to anyone who works by clicking, this family may as well not exist. Only MLINE even has an alias.
Autodesk describes it in four words on its MLINE page for the 2027 release: "Creates multiple parallel lines".
Type ML and press Enter, and the first line printed already tells you all three settings in force:
Current settings: Justification = Top, Scale = 300.00, Style = STANDARD
Specify start point or [Justification/Scale/STyle]:Read it before clicking and most of the usual trouble disappears. All three settings persist from the last time anyone used the command in that drawing.
The justification option decides where your clicks land
This is the part that surprises people. You click two points, but the two wall faces do not necessarily sit symmetrically about the line you clicked.
We drew three multilines of width 20 along three identical lines, changing only the justification, and measured each bounding box against the clicked line.
| Justification | Bottom of bounding box relative to the clicked line | Meaning |
|---|---|---|
Top | 20 lower | both faces sit below the clicked line |
Zero | 10 lower | the clicked line is the centre |
Bottom | exactly level | both faces sit above the clicked line |
The picture at the top of this article shows all three, with the clicked line drawn in red to make it visible.
Autodesk explains it the same way. For Top: "Draws the multiline below the cursor". For Zero: "Draws the multiline with its origin centered at the cursor". For Bottom: "Draws the multiline above the cursor".
For real floor plans Zero is the sensible choice, because a wall axis on a structural set is always a centreline. Leave it on Top and click along the grid, and the whole wall sits half a thickness off.
The scale option is the width, not a multiplier
The word "Scale" leads people to expect a multiplier, so they type 1 and watch the two faces collapse together.
We measured it with the bounding box: type a scale of 20 and the width comes out at exactly 20; type 40 and it comes out at exactly 40.
The reason sits in the style definition. Read straight from the drawing's own dictionary, the STANDARD style holds exactly two elements at offsets of +0.5 and −0.5. Their difference is 1, so whatever scale you give becomes the distance between the faces.
Put plainly: for a wall 220 thick, type a scale of 220. There is nothing else to work out.
Two special values were measured as well.
A scale of 0 gives a bounding box exactly 0 high, meaning the faces fall onto each other. Autodesk states it: "A scale factor of 0 collapses the multiline into a single line".
A negative scale still gives the width as its absolute value; we typed −20 and measured 20. What changes is the order of the elements, visible only when a style has faces of different colours or linetypes.
The mlstyle command: building your own wall type
The STANDARD style is two plain lines. For a three-layer wall, or faces in different colours, or a filled core, you have to declare a style of your own.
Type MLSTYLE, or go to Format → Multiline Style. In the dialog click New, give it a name, then under Elements add each face with its offset, colour and linetype.
Three things are worth remembering when declaring one.
First, declare offsets on a scale of one, putting the outermost faces at +0.5 and −0.5 as the standard style does. Then a scale equal to the real thickness is all you ever need.
Second, multiline styles live inside the drawing, not in the program. Send the drawing and the style travels with it, but start a new drawing and you declare it again. To carry one across, save it to an .mln file with the Save button and Load it in the other drawing.
Third, a style already in use cannot be edited. The dialog greys the Elements section out. To change it, delete every multiline using that style first, or build a new style instead.
The mledit command: sorting out wall junctions
Once the plan is drawn, the places where two walls meet carry surplus lines. Ordinary commands like TRIM will not cut a multiline the way you want, because the program treats the whole set as one object.
That job belongs to MLEDIT, at Modify → Object → Multiline. Autodesk summarises it on the -MLEDIT page for the 2027 release: "Edits multiline intersections, breaks, and vertices".
There is a command-line version too, and it is handier than the dialog because it lays every option out on one line. Type -MLEDIT and it asks, verbatim:
Enter mline editing option [CC/OC/MC/CT/OT/MT/CJ/AV/DV/CS/CA/WA]:Those twelve codes fall into five groups. The first three, CC, OC and MC, handle walls crossing in a cross shape: closed, open and merged. The next three, CT, OT and MT, do the same for tee junctions. CJ makes a corner joint. AV and DV add and delete a vertex. The last three cut and mend: CS cuts one element, CA cuts the whole set, and WA welds a cut back together.
Every option works the same way: pick the code, then click the two multilines in turn. Order matters for the tee group, because the one clicked first is the one that gets cut.
If you would rather not learn the family, there is a way round: explode the multiline and trim it like ordinary geometry. We measured it on the machine — typing X for EXPLODE breaks a multiline into separate LINE objects.
But once exploded it is no longer a multiline, and changing the thickness later means dragging each face. Joining loose lines back into one continuous outline is covered in our article on polylines in AutoCAD.
When to use it and when to draw another way
The mline command in AutoCAD is quick, but it does not suit every job. Three situations divide it fairly clearly.
Use it when drawing a whole plan from scratch. Walls of one thickness, running long, with many changes of direction. Set style and scale once and draw straight through, one pass per wall instead of two.
Use it when the thickness may still change. Because the set is one object, editing the scale in the Properties palette changes the whole run. Drawn as loose lines, each face has to be dragged.
Do not use it when the drawing already exists and you are adding a wall or two. OFFSET from an existing line is quicker and needs no junction work. Avoid it too when the drawing is going into other software, since a multiline is an AutoCAD-specific object that many programs read back as loose lines.
Three things people say that are not true
| What people say | What the 2027 release actually does |
|---|---|
| The scale is a multiplier so leave it at 1 | The scale is the width. The standard style has faces at ±0.5, so a scale of 220 gives a wall exactly 220 thick |
| The two faces always straddle the clicked line | Only on Zero. On Top both faces sit below it, on Bottom both sit above |
Trim junctions with TRIM as usual | You cannot. The whole set is one object, so junctions need MLEDIT |
One last note for anyone drawing plans with multiline styles of their own: set the style and the scale before drawing the first wall. Change them halfway and the walls already drawn keep the old settings. Other ways of drawing parallel lines are covered in our article on parallel lines in AutoCAD.
Frequently asked questions
What is the alias?
ML. Its two companions, MLSTYLE and MLEDIT, have no alias and no ribbon button at all.
How do I set the wall thickness?
Type the thickness straight into the Scale option. For a 220 wall type 220, because the standard style's faces are exactly one unit apart.
Why is my wall off the grid line?
Because the justification is Top or Bottom. Choose Justification then Zero so the clicked line becomes the wall centreline.
Why have the two faces merged into one line?
The scale is 0. Measured on the machine, the bounding box is exactly 0 high at that setting.
Which command trims wall junctions?
MLEDIT at Modify → Object → Multiline, not TRIM.
What do I get if I explode a multiline?
Separate LINE objects. But once exploded it is no longer a multiline, so the thickness can no longer be changed in one go.