The two orbital elements that determine the size and shape of a planetary orbit are: planet's equatorial diameter and rotation rate tilt of the planet's axis and orbital period planet's orbital eccentricity and semi-major axis planet's speed and inclination

planet's orbital eccentricity and semi-major axis

Explanation:

The eccentricity and the semi - major axis controls the size and shape of the orbit of the planet. The value for the semi major axis is equal to the half of largest diameter of the elliptical orbit.

The eccentricity controls the shape of elliptical orbit. It is the ratio of the center to the focus (sun) length and the semi - major axis length.