Drawing circles in AutoCAD takes three seconds and nobody needs a tutorial for it. The two questions that come with it are less obvious: how to place a circle tangent to two existing objects, and why the circle on screen looks like a many-sided polygon.
This article answers both, and covers dividing a circle and marking its centre. For the whole drafting workflow, see the AutoCAD for Construction course.
The circle command: the real prompt and three options
The CIRCLE page at Autodesk describes the command in two words: "Creates a circle". Type C and press Enter, and the prompt on AutoCAD 2027, copied from the screen, reads:
Specify center point for circle or [3P/2P/Ttr (tan tan radius)]:
Notice something most tutorials skip: the prompt offers three options, but the command has six methods. The other three are centre with radius, centre with diameter, and tangent to three objects. The first two hide inside the default branch; the third can only be reached from the Draw menu.
Click a point for the centre and AutoCAD asks for a radius. To enter a diameter instead, type D and press Enter, which saves halving the number in your head. This is exactly where mistakes creep in when the drawing quotes a diameter and the figure goes straight into the radius box.
Typing is often faster than clicking. Type C, Enter, the centre as x,y, Enter, then the radius. That suits a drawing that already has a grid and known figures, with no hunting for a point with the mouse.
Tangent tangent radius: the option worth remembering
Ttr stands for tangent tangent radius, and it is the most useful thing in the whole command. It places a circle tangent to two existing objects at a radius you give. Type T, Enter, pick the first object, pick the second, then type the radius.
A subtlety: where you click on each object decides which side the circle lands on. With two crossing lines, clicking in the upper corner gives the upper circle and the lower corner gives the lower one. Clicking near the intended tangency is the safe habit.
Tan Tan Tan places a circle tangent to three objects, and asks for no radius because three tangency conditions already fix it. That one is not on the prompt line; open the Draw menu, then Circle, then the last entry.
Both save real time at road junction fillets, at pipes curving around a column, and anywhere the drawing quotes a radius but no centre. Building one by hand and dragging it to look right is always a few millimetres out; these give the exact tangency from the start.
Knowing all six matters more than it sounds. Most people who draw circles in AutoCAD every day use exactly one method, then reach for construction lines and trimming whenever the geometry is defined by tangency instead of by a centre. Ten seconds spent on the right option saves several minutes of cleanup, and leaves geometry that is exact rather than merely close.
A circle is not an arc and not a polyline
The three look alike on screen but are three different object types, and later commands treat them differently.
A circle is a closed object storing exactly two things: a centre and a radius. An arc is part of one, storing a start and end angle as well; our article on drawing arcs in AutoCAD covers that. A polyline can contain curved segments but is fundamentally a chain of vertices, which is why it accepts a line width and a circle does not.
The difference shows up when measuring. Select a circle, run the area command, and the second figure comes back labelled Circumference rather than Perimeter. The label tells you what you selected, as our article on calculating area in AutoCAD explains.
VIEWRES: why the circle looks jagged and how to fix it
This is the second common question, and the answer is simpler than people fear. A circle that draws as a polygon is not a corrupt drawing and not a weak graphics card. It is how AutoCAD draws quickly: it approximates the curve with a chain of straight segments, and the VIEWRES command sets how many.
Type VIEWRES and press Enter. AutoCAD asks two questions, copied verbatim:
Do you want fast zooms? [Yes/No] <Y>:
Enter circle zoom percent (1-20000) <1000>:
Press Enter through the first. The second is the number that matters. On the machine at the Institute it sat at 1000, and the legal range is 1 to 20000. We dropped it to 20 and the facets were plain to see; we raised it to 2000 and the curve went smooth. Both images above are the same circle in the same view.
The default of 1000 is high enough for ordinary work. The people who meet the jagged look are usually working on a drawing that came from someone else with a low value saved in it, or on a very large circle seen close up. Either way the cure is the same one command.
Two things to remember. First, this is display only: the printed sheet is round either way, because the plotter rebuilds the curve from the data rather than from the screen. Second, a higher number means slower redraws on a heavy drawing, so do not simply push it to 20000 and forget it.
Marking the centre
Technical sheets want a centre mark, and two commands provide one. Type CENTERMARK and the prompt reads:
Select circle or arc to add center mark or [Layer]:
The mark this makes is associative: change the radius and the mark follows. That is the one to use on a set that will be revised.
The older command is DIMCENTER, with a shorter prompt:
Select arc or circle:
It draws a loose cross that follows nothing. One step quicker, but editing the circle means redrawing the mark.
How to divide a circle into equal parts
This comes up laying out bolts on a flange or stations along a curve. Use DIVIDE, whose first prompt is:
Select object to divide:
Pick the circle, type the number of parts, Enter. AutoCAD places points evenly around the circumference. A trap follows immediately: the points are drawn as an almost invisible dot by default. The PDMODE variable on the machine at the Institute sat at 0, which is the smallest dot style.
Fix it with DDPTYPE, choose a visible style such as a cross, and set a size. Then snap to Node to draw at exactly those points; our article on object snaps in AutoCAD covers the snapping.
To divide by a fixed distance rather than a count, use MEASURE. Same procedure, different final question.
One more caution on flanges: divide places points on the circumference, so a circle divided into eight gives eight positions starting at an arbitrary angle. If the drawing fixes where the first bolt goes, draw a construction line at that angle first and rotate the whole array to suit, rather than hoping the division happens to start in the right place.
A habit worth copying on structural sheets: divide, draw one small circle at the first point, then array it around the centre. The division only supplies positions; the objects that go into the set are the bolt circles. Deleting the points afterwards is safe, because nothing you drew depends on them.
Three things often repeated that are not true
| Often repeated | What the 2027 release does |
|---|---|
| A polygonal circle means a corrupt drawing | It is display only. Change VIEWRES and it is gone; the print was always round |
| The command only has the three methods on the prompt | It has six. Two hide in the default branch, one lives only in the menu |
| Tangency means drawing then dragging to fit | Ttr does it: pick two objects, give a radius, AutoCAD finds the tangency |
Frequently asked questions
Can I enter a diameter instead of a radius?
Yes. After picking the centre, type D and press Enter and the question changes to the diameter. Use it whenever the drawing quotes a diameter, to avoid halving it yourself and slipping.
I changed VIEWRES and the circle is still jagged. Why?
Try REGEN. The new value applies when AutoCAD rebuilds the display, and some drawings need to be pushed into doing it.
Will the jagged look print?
No. What the drawing stores is a centre and a radius, not a chain of segments. The plotter rebuilds the curve at its own resolution.
I divided a circle and no points appeared.
They are there, drawn in the smallest dot style. Type DDPTYPE, choose the cross style and set a size, and they show up.
How do I read the radius of an existing circle?
Select it and open the Properties palette, where Radius and Diameter sit next to each other. Or place a radial dimension, as covered in our article on dimensions in AutoCAD.