One calorie per cubic mile is almost exactly the same as one joule per cubic kilometer. Because a calorie is 4.185 joules and a cubic mile is 4.166 cubic km. And the density of the universe has finally been measured to the general satisfaction of astronomers, at 0.85 joule per cubic kilometer. This is what makes it flat, and matches the observed acceleration of expansion and the observed bumpiness of the CMB. As a rough size 0.85 is about one. And so roughly speaking the density of the universe is ONE joule per cubic km. And in old-timey units (for people who can think in calories and miles) that is about one calorie per cubic mile. Actually 0.85 but about. Tonight there will no doubt be some people on this planet who look up at the dark and think "hmmm, on average there is about a calorie in a cubic mile of that"