How to use the TRIM command in AutoCAD

The TRIM command trims objects back to a cutting edge, so lines fit precisely together.

With the TRIM command you remove the part of a line, arc, circle or polyline that extends beyond another piece of geometry. The geometry you trim up to is called the cutting edge. Trimming belongs, together with EXTEND (which lengthens objects to a boundary), among the most-used drafting operations in AutoCAD.

You start the command by typing TRIM and pressing Enter, or via the shortcut TR. On the ribbon you’ll find the button under the Home tab, Modify panel (Home > Modify). As soon as the command runs, the command line shows the current settings:

Command: TRIM
Current settings: Projection=UCS, Edge=None, Mode=Quick
Select object to trim or shift-select to extend or
[cuTting edges/Crossing/mOde/Project/eRase/Undo]:

The line “Mode=Quick” tells you which mode you are working in. This has become important since AutoCAD 2021 because the default behaviour changed then.

Virtually any ordinary object can serve as both cutting edge and object to be trimmed: lines, arcs, circles, ellipses, polylines, splines, rays, construction lines (xlines), text, regions and even the boundary of a hatch. Blocks and objects inside an external reference are not included; you trim those only in their own source file.

In Quick mode, all geometry acts as a cutting edge; in Standard mode you select the cutting edges yourself first.

AutoCAD has two trim modes. Which one is active is determined by the system variable TRIMEXTENDMODE. Since version 2021 the default is Quick, which works faster but behaves differently from the old method many users are used to. In Quick mode you don’t need to select boundaries first, which saves time for rapid clean-ups; in Standard mode you have more control because you decide which lines count as boundaries. Both modes exist side by side and you can switch between them in seconds.

If you want to go back to the old, two‑step method, set TRIMEXTENDMODE to 0:

Command: TRIMEXTENDMODE
Enter new value for TRIMEXTENDMODE <3>: 0

You can also switch while the command is running by using the mOde option (type O), without permanently changing the variable.

Trimming in Quick mode takes three steps: start TRIM, point to the parts to be trimmed away, and finish with Enter.

For everyday use in Quick mode, follow these steps:

1. Type TR and press Enter to start TRIM.
2. Move the mouse to the line segment you want to remove. The part up to the next intersection highlights.
3. Click to trim that part away. Repeat for each subsequent piece.
4. If desired, drag a fence (two points) or lasso across multiple lines to trim them all at once.
5. Press Enter, Spacebar or Escape to end the command.

If you want to immediately repeat the command, press Enter or Spacebar after finishing. AutoCAD will restart TRIM.

A practical example: you are creating a door opening in a wall of two parallel lines. Draw two short vertical lines where the opening should be, start TRIM and, in Quick mode, click the two wall segments between those lines. AutoCAD trims exactly the wall section between the two verticals and the opening is there. You use the same method for window frames, recesses in pipe drawings, and clipping crossing grid lines in a raster.

Select cutting edges yourself in Standard mode, where you first choose the boundary objects.

In a busy drawing you sometimes want to trim to a specific line and leave everything else alone. Switch to Standard mode then:

1. Start TRIM and type O for mOde.
2. Choose Standard.
3. Select the objects that may act as cutting edges and press Enter.
4. Now click the parts you want to trim back to those edges.

If you don’t select any cutting edge in step 3 and press Enter immediately, Standard mode still behaves like Quick mode and all objects count as edges. That is a handy middle ground.

Standard mode is especially nice when several lines lie close together and you only want to trim up to one of them. By precisely selecting that single line as the cutting edge, you prevent AutoCAD from trimming to the wrong intersection. In symmetrical parts, façade grids or installation drawings, this saves corrective work afterwards.

With the Edge option set to Extend, you can also trim to a cutting edge that does not physically touch the object.

Occasionally you want to trim up to a line that is just too short and does not really intersect the object. In Standard mode the system variable EDGEMODE controls this. At 0 AutoCAD works only with real intersections; at 1 it extends the cutting edge imaginarily until it meets the object.

Command: EDGEMODE
Enter new value for EDGEMODE <0>: 1

Inside the command you achieve the same via the Edge option, where you choose between Extend and No extend. Set Edge back to No extend when you are done, otherwise AutoCAD will later trim to boundaries you cannot see on screen, making it seem as if geometry is vanishing without reason.

The Crossing, Fence and eRase options give you more control without exiting the command.

The command line shows a series of options in square brackets during TRIM. The most important ones:

• Crossing (C): drag a rectangular crossing selection window over multiple objects.
• Fence (two empty points or dragging a line): everything the line touches is trimmed.
• eRase (R): delete loose objects without leaving TRIM. Useful for short leftovers that don’t intersect any cutting edge.
• Undo (U): reverse the last trim while the command stays active.
• Project (P): determines how AutoCAD projects in 3D. Set to UCS to solve most 3D trimming issues.

Watch out for a peculiarity of Quick mode: if you click an object that does not intersect any other line anywhere, it disappears completely instead of nothing happening. If you see an object vanish unintentionally, immediately type U to bring it back.

The U option inside the command only undoes the last trim. If you have already finished the command and want to undo a whole series of trim actions, use the separate UNDO command (shortcut Ctrl+Z). AutoCAD treats each completed TRIM session as a step, so pressing Ctrl+Z a few times returns you to the situation before the trimming.

Hold Shift while using TRIM to extend instead of trim.

TRIM and EXTEND are opposites and AutoCAD combines them within a single command. While TRIM is active, hold down Shift and click a line that is just too short. AutoCAD extends that line to the nearest boundary, as if you had used EXTEND.

It works the other way round too: start EXTEND (shortcut EX) and hold Shift to trim. This combination saves a lot of switching between commands when you are sizing a series of lines. If AutoCAD reacts slowly or the display stutters, the cause is often not the command but the file itself; our explanation on why AutoCAD becomes slow or freezes helps you track that down.

For two lines that should meet neatly at a corner, there is a quicker alternative than trimming and extending separately. Start FILLET (shortcut F), set the radius to 0 and click both lines. AutoCAD trims or extends both of them to form a sharp corner. If you hold Shift during FILLET, you force a radius of 0 regardless of the current setting.

Command: F
FILLET
Current settings: Mode = TRIM, Radius = 0.0000
Select first object or [Undo/Polyline/Radius/Trim/Multiple]:

Most trim problems are caused by a locked layer, a non‑intersecting cutting edge, or an incorrect projection.

If TRIM doesn’t work as expected, run through these causes:

• The object is on a locked layer. AutoCAD does not trim geometry on a layer with a padlock. Unlock the layer in the Layer Properties Manager.
• The lines don’t actually intersect. Two lines that visually almost touch but do not intersect cannot be trimmed to each other. Zoom in and check whether they truly cross.
• The object is inside an external reference (xref). Geometry in an xref cannot be trimmed with TRIM in the host file; you must edit it in the source file.
• Wrong projection in 3D. If Project is set to View or None while you are working in 3D, trimming may appear to fail. Set Project to UCS.
• The file is bloated or too heavy. Excess data slows down selections. Purge the drawing with the PURGE command to reduce your file size before large trimming operations.
• You are working in a layout. TRIM works both in model space and in a layout (paper space). If you click inside a viewport, you trim the model geometry; if you click on the layout itself, you trim the annotation on the sheet. So check which space you are in.

If it remains unclear how a specific option works, the official Autodesk documentation about the TRIM command describes each variant with examples. Once you have mastered the modes, you will trim a floor plan in a fraction of the time.