I'm against quantifying anything unless it's somehow necessary, including things like running and friends and "time." The Fitbit and everything else that's popular right now are against me. In the most recent New York Times Magazine, Gretchen Reynolds recapped an interesting study germane to these tendencies, in which Dr. Antony D. Karelis, a professor of exercise science at the University of Quebec at Montreal, quantified the caloric benefits of sex and qualified them as "moderate exercise."
Karelis had research subjects wear heart monitors during sex, and also during various types of exercise. He found that average sex was the metabolic equivalent of "playing doubles tennis or walking uphill" but slightly less than jogging—"though some men, according to their activity monitors, used more energy for brief periods during sex than they did jogging."
More numbers of note: "The sex also burned four calories per minute for men and three per minute for women, during sessions that ranged from 10 to 57 minutes, including foreplay. The average was 25 minutes." The average number of calories burned was 85.
Also, Reynolds says, "Ninety-eight percent of Karelis’s volunteers reported that sex felt more fun than jogging." She attributes that to two percent having unsatisfying sex, but it could also be uniquely satisfying jogging. Further study warranted.
This research is full of interesting data for conversation and self-reflection, though it's worth also noting, which the magazine did not, that the average participant in the study was 22 years old. Also, ten minutes is not much tennis. Does that even count as tennis? Anyway, what else can we quantify?