A new method for estimating lightning leader potential in negative stepped leaders from electric field changes during the first return stroke process in cloud-to-ground flashes is applied for determining the striking distance to a ground structure. This method may serve as an alternative to calculating the striking distance from formulas that relate it to the peak return stroke current. Presented are the characteristics of downward leaders (potential, vertical extent, and the length of the final step) and the charges transferred during return strokes; these were obtained from electric field measurements during a thunderstorm in Florida using the line charge model. The final step lengths of the leaders are compared with striking distances calculated using the peak current values of return strokes taken from National Lightning Detection Network data for the same flashes.