This command draws circles by two points, three points, and by tangent, tangent, and radius; it also converts arcs to circles.
Accessing the Command
command bar: circle
alias: c
menu bar: Draw  Circle
toolbar: Draw 
ribbon: Draw  Draw  Circles
: circle
You are prompted:
Select center of circle or [2Point/3Point/TTR/Arc/Multiple]: (Pick a point, or enter an option)
Set Radius or [Diameter] <x.xx>: (Pick a point, enter a distance, or type D to define the diameter)
The complete list of circle drawing methods is summarized by the Draw  Circle menu:
In the icons, the larger green dot indicates the starting point, the smaller green dots the additional pick points. When an icon has all small dots, then the pick order does not matter.
Command Options
Option 
Description 
Select center of circle 
Specifies the center of the circle:
The z coordinate is rarely entered, so most often you enter x,y coordinates. 
Diameter 
After you pick the center point, this prompt asks you to specifies the diameter of the circle: Diameter of circle  (enter a distance, coordinates, or pick a point) 
Set Radius 
After you pick the center point, this prompt asks you to specify the radius of the circle: Radius of circle  (enter a distance, coordinates, or pick a point) 
2Point 
Defines the circle by two points that you pick on its circumference; prompts you:
The abbreviation for this option is 2P. 
3Point 
Defines the circle by three points that you pick on its circumference; prompts you:
The abbreviation for this option is 3P. 
RadTanTan 
Defines the circle by two points that are tangent to other entities, along with the radius. A tangent is where a circle touches another entity. The Tangent entity snap is activated automatically during the first two prompts:
The abbreviation for this option is RTT. 
Arc 
Converts arcs to circles by closing them; prompts you: Select arc to convert to circle  (Choose an arc) 
Multiple 
Repeats the command until you press Esc. 
Procedures
Grips Editing
Circles can be edited directly through grips:

Select the circle. Notice that it has five grips.

Drag the grips to perform the following actions:
 Drag the quadrant grips to stretch the circle (increase and decrease the radius).
 Drag the center point grip to move the circle.
Related Commands
Ai_CircTan  draws a circle tangent to three entities.
Arc  draws arcs.
Change  changes the diameter of circles.
Ellipse  draws ellipses.
Join  joins arcs to create circles.
Donut  draws fat circles from polyline arcs.
DimRadius and DimDiameter  dimensions circles.
Center  snaps to the center of circles.
Quadrant  snaps to the 90degree points on the circumference of circles.
Tangent  snaps to the tangency of circles.