How to draw an ellipse in AutoCAD: three methods, the PELLIPSE variable and three things an ellipse cannot do

How to draw an ellipse in AutoCAD comes down to ELLIPSE, aliased EL. In a building drawing set, ellipses are bathtubs, basins, dining tables and pipes cut on a slant.

The command is easy to call, but two things about it cost people time and rarely appear in tutorials: one variable changes the kind of object the command produces, and because an ellipse has no radius, a whole set of familiar commands refuse it. To learn modelling and documentation end to end, see the AutoCAD for construction course.

The ellipse command in AutoCAD: three prompts, four options

The button sits in the flyout beside the Arc button on the Draw panel. Typing EL is quicker.

An ellipse is defined by two perpendicular axes, so the command asks three times.

The third prompt is the one most often misread. It asks for the distance from the centre to the edge, a semi-axis, not the whole axis. A bathtub 750 wide takes 375.

The four options and what each is for:

How to draw an ellipse in AutoCAD: a 1700 by 750 bathtub

This is the ellipse drawn most often on a building plan. Three steps:

1. Type EL and Enter. Pick one end of the long axis, snapping to the inside face of the wall.
2. Type @1700,0 and Enter. That is the other end of the long axis.
3. Type 375 and Enter. The ellipse appears, centred between the two points you picked.

Step three is 750 halved. Type 750 and you get a bathtub 1500 wide, twice what you wanted.

To snap accurately onto a wall face, object snap has to be on — see Object snap in AutoCAD.

Starting from the centre, and giving a rotation instead

The other two options come up less often but each solves its own problem.

Start from the centre. Type EL, then C, pick the centre, pick one axis end, then give half the other axis. This suits the case where the centre is known but the edge is not, such as a basin set exactly mid-worktop.

Give a tilt angle instead of a semi-axis. Type R at the third prompt and the command asks for an angle. Picture a circle rotating about the first axis: at 0 degrees it stays a circle, and the further it turns the flatter the shape becomes.

The reference states the limit on that angle, and the numbers are worth remembering.

The details are on the ELLIPSE (Command) page.

One variable changes what the command draws

This is what puzzles people: the same AutoCAD release draws an ellipse on one machine and a polyline on another. The cause is the PELLIPSE system variable.

It is an integer, 0 by default, and saved in the drawing rather than on the machine. Opening someone else's file brings their setting with it.

There is an immediate tell: set PELLIPSE to 1 and the Arc option disappears from the prompt, because a polyline has no concept of an elliptical arc. A prompt missing Arc is not a broken installation — type PELLIPSE then 0 to restore it.

In exchange, a polyline ellipse can be edited with PEDIT and offset like any other polyline. See the PELLIPSE (System Variable) page.

An ellipse has no radius, and three consequences

A circle has one radius. An ellipse has two different semi-axes, so every command that wants a single radius figure refuses it. Three practical consequences:

OFFSET will not give a concentric ellipse. Geometrically, the parallel curve of an ellipse is no longer an ellipse. The command still runs but returns a different object type. For a concentric ellipse, COPY then SCALE instead.

No diameter dimension. DIMDIAMETER needs a circle or an arc. An ellipse takes two linear dimensions, one per axis — which is also how a real drawing set dimensions a bathtub.

But the area does read. Select the ellipse and open the Properties palette with Ctrl and 1: area and perimeter are both there, with no measuring command needed.

The rule that follows: draw genuinely round things with CIRCLE, and use ELLIPSE only for things that really are oval. Drawing a round column as an ellipse throws away both the diameter dimension and the offset.

Measuring and dimensioning an ellipse

Once it is drawn the numbers have to reach the sheet, and an ellipse has no dimensioning command of its own. Three ways to read it:

• The Properties palette (Ctrl and 1): area, perimeter and both semi-axes.
• The LIST command, aliased LI: opens the text window with the object type and its properties. It is also the quick way to check whether what you have is a true ellipse or a polyline.
• Dimensioning: use DIMLINEAR twice, once per axis. Snapping to the axis ends needs object snap on, since an ellipse carries snap points at its four axis vertices.

Telling chord, arc length and radius apart on a curve is covered in How to measure an arc in AutoCAD.

Isocircle: the isometric ellipse

Here is where ellipses turn up unexpectedly. A circle lying on the face of an object does not stay a circle in an isometric view — it becomes an ellipse.

Drawing that by hand is painful. AutoCAD has a dedicated option, but it only appears while isometric mode is on. Comparing the two prompts of the same command shows it plainly.

Autodesk states the condition directly: "The Isocircle option is available only when an isometric plane is active", on the About 2D Isometric Drawing page.

Turn the mode on with ISODRAFT and pick one of the three planes: Left, Top or Right. The command has no option named Off — choose Orthographic to turn it off. It also supersedes the older ISOPLANE command.

Four steps:

1. Call ISODRAFT and pick the plane the circle lies on.
2. Call EL and type I for Isocircle.
3. Pick the centre of the circle.
4. Enter the true radius of the circle, not the radius of the ellipse.

How big is that ellipse? The answer is measurable. Draw an isocircle of radius 700 and read back the object it produced:

Those figures are not odd by accident. 1.2247 is the square root of 1.5, 0.7071 is one over the square root of two, and 1.7321 is the square root of three. So the major axis is always √3 times the minor axis, on all three planes.

Remembering √3 is enough to check by eye: an ellipse on an isometric drawing that looks too round or too flat was not drawn by Isocircle.

Pick the wrong plane and the ellipse still appears, but leaning the wrong way. That is hard to spot at a glance, so look at the crosshairs once before calling the command. Press F5 to cycle through the three planes.

Frequently asked questions

Which command draws an ellipse in AutoCAD?

ELLIPSE, aliased EL. The button is in the flyout beside the Arc button on the Draw panel of the Home tab.

Why does my ellipse come out twice the size I wanted?

Because the third prompt asks for half the axis measured from the centre, not the whole axis. A bathtub 750 wide takes 375.

Why is the Arc option missing from my prompt?

PELLIPSE is set to 1, so the command makes a polyline rather than a true ellipse. Type PELLIPSE then 0 to restore it.

OFFSET does not give me a concentric ellipse. What do I do?

The parallel curve of an ellipse is not an ellipse, so the command returns a different object type. Use COPY then SCALE instead.

How do I dimension the diameter of an ellipse?

You cannot, because an ellipse has no radius. Dimension it with two linear dimensions, one for the major axis and one for the minor.

How do I draw a circle on an isometric drawing?

Turn on ISODRAFT, pick the plane, then call EL and choose Isocircle. Enter the circle's true radius and the command works out both ellipse axes.

Related articles

• How to draw a rectangle in AutoCAD — the REC command, eight options and the settings that persist
• How to draw an arc in AutoCAD — eleven construction methods and the radius trap
• How to measure an arc in AutoCAD — telling chord, arc length and radius apart
• What is AutoCAD — a handbook for people working in construction