ArcGIS Pro 2.7 API Reference Guide
Length Property (EllipticArcSegment)
Example 

ArcGIS.Core.Geometry Namespace > EllipticArcSegment Class : Length Property
Gets the 2D length of this elliptic arc segment.
Syntax
public override double Length {get;}
Public Overrides NotOverridable ReadOnly Property Length As Double
Remarks
If the 3D length of the elliptic arc is required, create a polyline from the arc segment and use the Polyline.Length3D property.
Example
// retrieve the curve's control points
EllipticArcSegment arc = EllipticArcBuilder.CreateEllipticArcSegment(arcSegment);
MapPoint startPt = arc.StartPoint;
MapPoint endPt = arc.EndPoint;
Coordinate2D centerPt = arc.CenterPoint;
bool isCircular = arc.IsCircular;
bool isMinor = arc.IsMinor;
bool isCounterClockwise = arc.IsCounterClockwise;
bool isCurve = arc.IsCurve;
double len = arc.Length;
double ratio = arc.MinorMajorRatio;

double semiMajorAxis, semiMinorAxis;
// get the axes
arc.GetAxes(out semiMajorAxis, out semiMinorAxis);
// or use the properties
// semiMajorAxis = arc.SemiMajorAxis;
// semiMinorAxis = arc.SemiMinorAxis;

double startAngle, centralAngle, rotationAngle;
// or use QueryCoords to get complete information
arc.QueryCoords(out centerPt, out startAngle, out centralAngle, out rotationAngle, out semiMajorAxis, out semiMinorAxis);

// use properties to get angle information
//double endAngle = arc.EndAngle;
//centralAngle = arc.CentralAngle;
//rotationAngle = arc.RotationAngle;
//startAngle = arc.StartAngle;
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

EllipticArcSegment Class
EllipticArcSegment Members