A line needs to be exactly 500 longer. There is no boundary to extend it to, and redrawing it is not worth the trouble. That is precisely the job of the lengthen command in AutoCAD.
This article follows the order you meet in practice: where to start the command, what it asks at each step, and only then the advanced options and a worked example. Every prompt is copied verbatim from AutoCAD 2027 at the Institute. For the full set of editing commands, see the AutoCAD for Construction course.
Where to start the lengthen command in AutoCAD
Four ways in, read straight out of the 2027 configuration files.
| Route | Detail |
|---|---|
| Full command | LENGTHEN |
| Alias | LEN |
| Ribbon | Home → Modify → Lengthen |
| Classic menu | Modify → Lengthen |
| Toolbar | no button anywhere |
That last row is worth noting. The command sits on no toolbar at all, so anyone who works by clicking buttons will not find it. Even the ribbon button lives inside the Modify panel's drop-down, behind the little arrow.
The alias comes from the line LEN, *LENGTHEN in the alias file. Adding aliases of your own is covered in our article on command aliases.
The prompts, step by step
This is where most people get stuck, because the command asks for the number first and the object second, the reverse of most editing commands. The table below is one complete run, with the middle column copied verbatim.
| Step | What the program asks | What you do |
|---|---|---|
| 1 | Select an object to measure or [DElta/Percent/Total/DYnamic] <Total>: | Type DE and press Enter |
| 2 | Enter delta length or [Angle] <0.0>: | Type 500 and press Enter |
| 3 | Select an object to change or [Undo]: | Click the line, near the end you want to grow |
| 4 | Select an object to change or [Undo]: | Click the next line, or press Enter to finish |
Two things follow from that table.
Step 1 hides a trap. Pick an object here without choosing an option and the command simply reports its length and stops, changing nothing. The word measure in the prompt says exactly that. People conclude the command is broken; in fact they have just used it as a quick length check.
Steps 3 and 4 repeat. Enter the number once, then click line after line, one click each. That is why this command is so much faster when a dozen lines all need the same treatment.
The delta option, the percent option and the total option
The four words in square brackets at step 1 are four ways of stating the number. Each has its own follow-up prompt, copied verbatim.
| Option | Type | Next prompt | Meaning |
|---|---|---|---|
DElta | DE | Enter delta length or [Angle] <0.0>: | add or subtract this much |
Percent | P | Enter percentage length <150.0>: | set as a percentage of the current length |
Total | T | Specify total length or [Angle] <1234.0>: | set the final length directly |
DYnamic | DY | Select an object to change or [Undo]: | drag with the cursor, no number |
All four run on the same line of exactly 2000.
| Entered | Length measured |
|---|---|
DElta 500 | 2500 |
DElta −500 | 1500 |
Percent 150 | 3000 |
Total 1234 | 1234 |
Four rows, four numbers that check with mental arithmetic. 500 onto 2000 gives 2500; minus 500 gives 1500; a hundred and fifty percent of 2000 is 3000; and Total ignores the old length and sets the new one.
The second row is the one worth remembering: a negative value shortens rather than raising an error, so one command covers both directions.
The advanced choice: Angle, and the included angle of arcs
Two of the prompts above carry an extra word, Angle, that almost nobody uses. It appears only under DElta and Total, and it means something only for an arc: instead of stating a length you state the included angle.
Autodesk describes the whole command in one line on the LENGTHEN page: "Changes the length of objects and the included angle of arcs". The second half of that sentence is this option.
Without Angle, the number still means arc length, not a straight-line distance.
| On an arc of radius 1250 | Before | After DElta 500 |
|---|---|---|
| Included angle | 106.26 degrees | 129.1 degrees |
That checks by hand. Adding 500 of arc on a radius of 1250 must increase the angle by 500 divided by 1250 radians, or 22.9 degrees; added to 106.26 that gives 129.2 degrees, matching what the program returned.
A worked example: grid lines overshooting by exactly 500
A real task on a structural drawing. The grid is drawn but the ends overshoot the building by varying amounts, and every axis needs exactly 500 of overshoot at both ends.
Six keystrokes, and no temporary boundary to draw.
Command: LEN (or type LENGTHEN)
Select an object to measure...: DE
Enter delta length...: 500
Select an object to change...: click the TOP end of axis 1
Select an object to change...: click the BOTTOM end of axis 1
Select an object to change...: click axis 2, axis 3, ...
Select an object to change...: Enter to finishThe point is that the 500 is entered once. Each end after that is a single click, and because the end nearest the click is the end that grows, both ends of the same axis can be done one after the other without restarting the command.
If every axis must finish at the same overall length, use Total instead of DElta — provided the axes started out equal.
A second example shows the percent option earning its place. A detail drawn at the wrong scale needs every leader line three quarters of its current length: enter P, then 75, then click each leader. No measuring, no arithmetic, and the proportions between them stay exactly as drawn.
Which end moves: the one you click nearest
The most practical question of all, measured in both directions to be sure.
The same line running from 0 to 2000, the same 500 added, only the pick point different.
| Clicked nearer | Left end afterwards | Right end afterwards |
|---|---|---|
| The right end | 0 | 2500 |
| The left end | −500 | 2000 |
Two rows, exactly opposite. The rule fits in one sentence: the end nearest your pick is the end that changes, and the other stays put.
That holds for all four options. With Total the end far from your pick acts as the fixed mark, and the new length is measured from there.
Not every object can be lengthened
On a circle the program answers with a single line, copied verbatim.
Cannot LENGTHEN this object.
Reasonable, since a circle is closed and has no end to pull. A proper pair makes it clearer: the same kind of object, differing only in being closed or open.
| Object tested | Result |
|---|---|
| A closed polyline | Cannot LENGTHEN this object. |
| An open polyline | lengthened, still a three-vertex polyline |
So the rule is not about the object type but about whether it has an endpoint at all. A closed polyline has to be opened first, which is covered in our article on polylines in AutoCAD.
How it compares with the extend command and its neighbours
Four commands that get used in each other's places, set side by side.
| Command | Needs | Result |
|---|---|---|
LENGTHEN | a number | longer or shorter by exactly that |
| The extend command | an object as boundary | stops exactly at the boundary |
| The trim command | an object as boundary | cuts the surplus away |
| The stretch command | a crossing window | moves a whole end by a vector |
The rule for choosing: when a line already exists to stop against, use the extend command or trim to it. When all you have is a number, use this one.
One more difference only shows up on a busy drawing. The stretch command moves everything caught in its crossing window, so reaching for it to lengthen a single line usually drags neighbours along with it. This command touches one object per click and nothing else, which is why it is the safer tool inside a finished drawing.
And when you only want to know a length rather than change it, pick the object at step 1 as described above. For the distance between two arbitrary points, use the distance command, aliased to DI from the line DI, *DIST in the same alias file.
Three things often repeated that are not true
| Often repeated | What the 2027 release actually does |
|---|---|
| It only lengthens; shortening needs another command | A negative value shortens at once, 2000 down to 1500 |
| Which end grows is up to the program | The end nearest the pick changes, measured in both directions |
| For an arc the number is a straight-line distance | It is arc length; the angle grew by length divided by radius |
Frequently asked questions
Where do I start the command?
Type LEN, or use Home → Modify → Lengthen on the ribbon, or Modify → Lengthen on the classic menu. There is no toolbar button for it.
Why does nothing happen when I pick an object?
Because you skipped the option step. Picking at step 1 only reports the length, exactly as the word measure in the prompt says.
How do I shorten something?
Still the DElta option, but with a negative value. A 2000 line entered as minus 500 comes out at exactly 1500.
Why did the line grow the wrong way?
Because you clicked the other half. The end nearest the pick point is the end that changes.
Why will a circle not lengthen?
The program answers Cannot LENGTHEN this object. A closed shape has no endpoint to pull.