AutoCAD Tip: Create Accurate Arc Length Dimensions with DIMARC in AutoCAD

Arc length dimensions communicate the true distance measured along an arc, rather than the straight-line chord distance between its endpoints. They are especially useful for curved fabrication, site layouts, piping, architectural details, and any drawing where the developed distance along a curve matters.

In AutoCAD, use the DIMARC command to create an arc length dimension quickly and accurately.

• Type DIMARC at the Command line.
• Select the arc, arc segment of a polyline, or arc portion of a circle.
• Move the cursor to position the dimension line.
• Click to place the dimension.

AutoCAD displays an arc symbol above the dimension value by default. This symbol distinguishes the measured curve length from a linear or chord dimension, helping reviewers, fabricators, and contractors interpret the drawing correctly.

Choose the right geometry. An arc length dimension should be used when the actual material, travel, or layout distance follows the curve. For example, if a handrail bends around a radius, the fabrication length is based on the arc length—not the horizontal or straight-line distance. Likewise, a curved curb, duct transition, or bent plate often requires an arc length callout for accurate construction.

For clean, standards-based results, consider these practical settings:

• Use an appropriate dimension style: Set text height, arrow size, units, and precision in DIMSTYLE before placing dimensions. Consistent styles make curved dimensions read as clearly as linear dimensions.
• Control precision carefully: Display only the number of decimal places required by the project. Excessive precision can imply unrealistic manufacturing or field tolerances.
• Keep dimensions outside the geometry: Place the arc length dimension where its extension lines and text do not conflict with center marks, hatches, leaders, or nearby notes.
• Use annotative dimensions when needed: In drawings with multiple viewport scales, annotative dimension styles help maintain readable text and symbols across layouts.
• Check associativity: Associative dimensions update when the arc changes. This is valuable during design revisions, but it depends on selecting actual arc geometry rather than drawing disconnected linework.

When dimensioning a partial arc from a circle, make sure the intended arc segment is clearly defined. If necessary, use visible endpoints, center marks, or supplementary radius dimensions so there is no ambiguity about which portion of the circle the arc length refers to. Avoid placing an arc length dimension on a full circle when a diameter, circumference note, or other annotation would communicate the design intent more effectively.

A useful workflow is to add the radius dimension first, then add the arc length dimension only where the curved distance is functionally important. The radius explains the shape; the arc length explains the distance along that shape. Together, these dimensions reduce interpretation errors.

Before plotting, inspect the layout at the final sheet scale. Confirm that the arc symbol is visible, dimension text is not obscured, and extension lines clearly identify the measured curve. A quick review can prevent costly questions from the field.

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