To find the eccentricity of an ellipse,use the formula

E = √(1-b²/a²)

where E is the eccentricity a is the length of the semi major axis (Longer axis) B is the length of the semi minor axis (shorter axis) eccentricity E indicates how much the ellipse deviates from being a circle. when E = 0 the shape is a perfect circle and as E approaches one the ellipse becomes more elongated