You select two lines, type J, and AutoCAD reports "0 objects joined". Another time two lines sit a full 200 units apart and join anyway. The join command in AutoCAD follows two quite different rules depending on what you select, and without knowing them you are left guessing.
This article works through six examples you can repeat on your own machine, each with the exact message AutoCAD prints, so you can recognise every case the moment it appears. For the whole drafting and editing toolkit, the Institute runs an AutoCAD course for construction.
What JOIN does
Autodesk sums it up in one line: "Joins the endpoints of linear and curved objects to create a single object."
The list of objects it accepts is equally explicit on the JOIN page: "Select lines, polylines, 3D polylines, arcs, elliptical arcs, helixes, or splines."
Notice that circles are not on that list. Some tutorials say JOIN turns circles into a polyline. A circle is already closed and has no endpoints to join.
Where to start it
Read straight from the 2027 configuration files.
| Entry point | What to use |
|---|---|
| Full command | JOIN |
| Alias | J |
| Ribbon | Home → Modify → Join |
| Classic menu | Modify → Join |
The prompts, step by step
The prompts below are quoted exactly as the 2027 release prints them when you type the command.
| Step | The prompt | What you do |
|---|---|---|
| 1 | Select source object or multiple objects to join at once: | Pick the first object |
| 2 | Select objects to join: | Pick the rest, then Enter |
| 3 | 2 lines joined into 1 line | AutoCAD reports the result |
The message at step 3 is the most useful thing on screen. There are three forms.
| Message | Meaning |
|---|---|
2 lines joined into 1 line | Two lines became one line |
2 objects converted to 1 polyline | Objects of different direction or type became one polyline |
0 objects joined, 2 objects discarded from the operation | Nothing joined |
When you see objects discarded from the operation, the endpoints did not meet in the way the rule for that object type demands. The examples below show exactly what that rule is, and the table sums it up in advance.
| What you select | Gap allowed? | Result |
|---|---|---|
| Collinear lines | Yes, even 200 units | One line |
| Lines meeting at a corner | No | One polyline |
| A line and an arc | No, not even 0.000001 | One polyline |
| Two arcs, same centre and radius, end to end | They touch | One arc |
| A single arc with the cLose option | Not applicable | One circle |
A note for LISP writers. Called as (command "_.JOIN" ...) from a LISP routine, AutoCAD uses the older prompts Select source object: and Select lines to join to source:. In that older form two perpendicular lines that touch are still rejected, even though typing the command joins them.
Examples 1 and 2: join lines in AutoCAD, and collinear lines with gaps
The first two examples show rule one: collinear lines are allowed a gap.
Example 1 — collinear, touching. Draw a line from 0,0 to 500,0 and another from 500,0 to 1000,0. Type J, pick both, Enter. AutoCAD reports 2 lines joined into 1 line and you are left with one line, 1000 long.
Example 2 — collinear, 200 apart. Draw 0,0 to 400,0 and 600,0 to 1000,0. Do the same. The result is still one line, 1000 long; the 200 gap is filled.
Autodesk says exactly this: "The line objects must all be collinear, but can have gaps between them."
This is handy when cleaning up a drawing. A wall line chopped into several collinear pieces comes back as one with a single command, and the result is a line, not a polyline, so every line-based tool still works on it.
Example 3: perpendicular lines into a polyline
Rule two starts here: objects in different directions must meet exactly at their endpoints.
Draw 0,0 to 1000,0 and 1000,0 to 1000,500. They meet at the corner 1000,0. Type J, pick both, Enter. AutoCAD reports 2 objects converted to 1 polyline: the two lines are now one L-shaped polyline.
Now repeat with the vertical line starting at 1000,100 instead, leaving a 100 gap at the corner. AutoCAD reports 0 objects joined, 2 objects discarded from the operation. No gap is forgiven.
So for two perpendicular lines that do not yet meet, JOIN is the wrong tool. Close the corner first with a zero-radius fillet, or hold Shift while picking the second line, as described in our article on the FILLET command. Once the corner is closed, J joins it.
Example 4: two crossing lines
Draw 0,0 to 1000,0, and a vertical line from 500,-300 to 500,300 crossing its middle like a plus sign. Type J, pick both.
AutoCAD reports 0 objects joined, 2 objects discarded from the operation. The lines cross in the middle and do not meet at an endpoint, so there is nothing to join.
Usually what people actually want here is to cut off the overhang first. Trim it with the TRIM command so the two lines only touch at one end, then use J.
Example 5: join a line and an arc, and the one-millionth trap
This is the example most worth trying, because it shows how strict rule two is.
Draw a line from -1000,500 to 0,500. Then draw an arc centred on 0,0, radius 500, from 0 to 90 degrees, so its upper end sits exactly at 0,500. Type J, pick both. AutoCAD reports 2 objects converted to 1 polyline, and the new polyline is 1,785.40 long: 1000 plus a quarter of the circumference of a radius-500 circle.
Now repeat with the line lifted by just 0.000001 units. AutoCAD reports 0 objects joined. A gap of 0.0001 or 0.01 gives the same answer.
| Gap between line and arc | Result |
|---|---|
| 0 — exactly touching | 1 polyline, 1,785.40 long |
| 0.000001 | Not joined |
| 0.0001 | Not joined |
| 0.01 | Not joined |
Your eye cannot tell these cases apart, but AutoCAD can. When a line and an arc refuse to join, their endpoints are almost certainly slightly apart. Turn on the Endpoint object snap and drag the line end onto the arc end.
Two arcs sharing a centre and radius, lying end to end, join into a single arc. An arc from 0 to 90 degrees plus one from 90 to 180 becomes one arc from 0 to 180.
Example 6: join an arc into a circle
Few people know this option. Draw an arc centred on 0,0, radius 500, from 0 to 270 degrees. Type J, pick only that arc, and press Enter at Select objects to join:.
AutoCAD then asks Select arcs to join to source or [cLose]:. Type L and Enter. It reports Arc converted to a circle. and the arc becomes a full circle with the same centre and radius.
Autodesk describes it as "The Close option converts the source arc into a circle." It is far quicker than erasing the arc and redrawing a circle, and the centre and radius stay exact.
JOIN or PEDIT
Both can join, but the results differ.
JOIN | PEDIT then Join | |
|---|---|---|
| Collinear lines | Become a line | Become a polyline |
| Touching objects in different directions | Become a polyline | Become a polyline |
| Gaps | Forgiven only for collinear lines | Has a fuzz distance setting |
When pieces miss each other slightly at the corners, PEDIT with a fuzz distance is the right choice. Details are in our article on polylines in AutoCAD.
Three things often repeated that are not true
| Often heard | What the 2027 release actually does |
|---|---|
| Lines drawn with LINE cannot be joined | Two lines join into one line, or into a polyline if they turn a corner |
| JOIN can join circles | Circles are not among the objects JOIN accepts |
| Only collinear lines can be joined | Perpendicular lines touching at a corner join into a polyline |
Frequently asked questions
What is the alias for the join command in AutoCAD?
J. Pick the objects and press Enter.
Why does it say "0 objects joined"?
The objects do not meet exactly at their endpoints. Only collinear lines are allowed a gap; everything else must touch exactly.
Do two collinear lines become a line or a polyline?
A line. Only objects in different directions or of different types become a polyline.
Can I turn an arc into a circle?
Yes. Type J, pick only the arc, press Enter, then type L for cLose.
A line and an arc look joined but will not join. Why?
They miss by a tiny amount. A gap of just 0.000001 is rejected, so snap the line end onto the arc end with Endpoint.
How do I join two perpendicular lines that do not touch?
Close the corner first with a zero-radius fillet, then use J.