How do I draw an arc by radius in AutoCAD?

Use the ARC command and choose a mode that specifies radius, such as Start–End–Radius. Pick the start and end points, then enter the exact radius value.

How can I draw an arc with a specific length?

Use an ARC method that allows length control, such as Start–End–Length. After selecting the start and end points, type the desired arc length.

How do I create a tangent arc to an existing line or circle?

Start the ARC command and choose a tangent option to ensure the new arc remains tangent to the selected object.

Why is my arc going the wrong direction and how do I flip it?

Arc direction depends on pick order and angle sign. Reverse the point order or use a different input method such as center or angle to correct the direction.

How do I fix the 'arc too small' or 'invalid radius' error?

This occurs when the requested radius is geometrically impossible given the selected start and end points. Adjust the radius or reposition your points.

What’s the shortcut or alias for the ARC command?

The default alias is A. You can customize aliases in the acad.pgp file if you want a different shortcut.

When should I use an arc instead of a circle?

Use an arc for partial curves and controlled transitions. Use a circle for full closed curves or reference geometry.

What are best practices for using arcs in architectural plans?

Ensure door swings, ramps, and archways follow consistent standards for layers, linetypes, and lineweights. Use tangent or fillet transitions to maintain clean geometry.

AutoCAD ARC Command

ARC Command Access

COMMAND LINE: ARC

DEFAULT KEYBOARD SHORTCUT: A

RIBBON: HOME | DRAW TAB | ARC

Drawing Methods with AutoCAD ARC Command

An arc is a portion of the circumference of a circle, or a continuous portion of a curved line. Arcs often connect ends of lines with a curve between them.

Simple arcs can be initiated from the command line. The command ribbon provides ten methods to draw an arc in a pull-down menu.

1. 3-Point

Initiate the ARC command in 3-Point mode, then enter three points the arc will pass through. The first point is the beginning of the arc, the second point is a point the arc will pass through, and the third point is the end of the arc.

2. Start, Center, End

Initiate the ARC command in Start Center End mode, then enter three points the arc will pass through. The first point is the beginning of the arc, the second point is the center if the arc length, and the third point is the end of the arc.

3. Start, Center, Angle

Initiate the ARC command in Start Center Angle mode, then select the start of the arc, the center of the arc, and the angle of the arc.

4. Start, Center, Length

Initiate the ARC command in Start Center Length mode then select the start point of the arc, the center of the arc, and the length of the arc.

5. Start, End, Angle

Initiate the ARC command in Start End Angle mode, then enter the start point of the arc, the end point of the arc, then the angle the arc will complete.

6. Start, End, Direction

Initiate the ARC command in Start End Direction mode, then enter the start point of the arc, the end point of the arc, then direction of the arc.

7. Start, End, Radius

Initiate the ARC command in Start End Radius mode and enter the start point of the arc, the end point of the arc, and the radius of the arc.

8. Center, Start, End

Initiate the ARC command in Center Start End Mode, then pick the center of the arc, the start point of the arc, then the end point of the arc.

9. Center, Start, Angle

Initiate the ARC command in Center Start Angle mode then pick the center of the arc, the start point of the arc, then the angle the arc will sweep.

10. Center, Start, Length

Initiate the ARC command in Center Start Length mode, then pick the center of the arc, the start point of the arc, then enter the length of the arc.

Arc Frequently Asked Questions (FAQs)

What is the ARC command used for in AutoCAD?

The ARC command is used to draw curved segments of circles. It supports multiple input methods so you can define an arc by its radius, endpoints, included angle, tangent conditions, or length, depending on your design needs.

Which ARC drawing method should I start with?

For most beginners, Radius and 3-Point are the best starting methods. Use Radius when you know the curvature you need. Use 3-Point when geometry or snapping drives the start, a point along the arc, and the end.

Are all ARC methods still relevant in current AutoCAD versions?

Some older variants are rarely used, but the core methods like Center-Start-End, 3-Point, Radius, and Tangent-based options are still very relevant. Focus on the methods that match how you actually design—smooth transitions, known radii, or snapping between existing geometry.

How do I decide which ARC method is best for a specific situation?

Think about what you know up front. If you know a radius and one or two key points, use the Radius or Center-based methods. If you’re fitting an arc between existing lines, try the Tangent or 3-Point options. For regulated curve lengths, choose a length-driven method.

Can I switch between line and arc workflows smoothly?

Yes. Many workflows mix LINE and ARC. You can draw a framework with LINE, then add arcs using tangent or endpoint snaps. You can also convert segments to polylines so line and arc pieces edit together as one continuous object.

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Written by

Scott

Scott Ogren, PE first used AutoCAD in 1993 while in college studying civil / structural engineering.

In 2002, I founded Ogren Engineering and have been working for myself since. AutoCAD and drafting skills are a requirement to work for my firm. Over the years, I have coached, tutored, and taught many people how to use and become proficient with AutoCAD.

Ogren Engineering: https://ogreneng.com/

In addition, Scott has written software to perform the lateral analysis of a wood-framed building.

Shearwall Pro: https://shearwallpro.com/

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AutoCAD ARC Command