To convert to watts multiply by 2. Positive for uphill, negative for downhill. Assume that for most bicyclists Cd is the same. Cd changes with the addition of fairings front and rear.
Frontal area changes with the size of the rider and position.
Hands on the top of the handle bar is the largest area. Hands on the brake hoods on a road bike or on the bar ends on a mountain bike are next. Hands on the drops on a road bike are next, and lowest exposed frontal area is achieved on aero bars. The following table gives initial guesses and test results for correcting factors to change the Kd. Based on tables of height and weight.