The term "calorie" is not to be confused with Calorie (capital C), which is generally used to describe food nutritional value. The term "Calorie" is actually a kilocalorie, or 1000 calories. A calorie is defined as the amount of heat required to raise the temperature of 1 gram of water 1 degree Celsius.
Physicists usually measure energy in joules rather than calories. Power is generally measured in watts. A watt is defined as 1 joule per second. This means that 1 joule expended in a full second equals 1 watt. If it were expended over 2 seconds, it would be 1/2 watt; if 1 joule is expended over 1/3 seconds, then it is 3 watts, etc.
1 calorie = 4.186 joules
The number of joules a weapon directs to a target determines how much work it can do. For example, to raise the temperature of the target, a certain number of joules has to be added to it. The power level is also important, as the work done on the target has to be done in a limited amount of time. If a lot of energy is added to the target over a long period of time, the heat may be radiated away before it can do any damage. If a small amount of energy is added at a very fast rate, the power level may be high, but little work will be done. Turbolasers are high energy and high power weapons. This may also help penetrate enemy shields, as the weapon's energy may be delivered faster than the shields can regenerate (even in fractions of a second).
In The Empire Strikes Back, a Star Destroyer (ISD) was witnessed clearing asteroids from its path by precise TL hits. Since we can estimate the size of these asteroids, and we can safely judge the chemical makeup of the asteroids, this becomes a reasonably accurate piece of information to judge the energy delivered by these specific TL bolts.
The bolts fired in the earliest asteroid-vape scene in film were mostly middle sized TL bolts (see Turbolaser Characteristics for more information about TL bolt sizes). Longer TL bolts were seen in this scenes as well, but were less frequent. The heavy dorsal turrets were never used.
Note that the asteroid this large-sized TL bolt has just hit is melting (and subsequently vaporised), and the TL bolt passed through, retaining its original shape, continuing on its original course. This implies that the energy contained in this bolt is much higher than the amount required to vaporise the asteroid. The bolt is passing another asteroid (in the lower-right corner of the image) that appears in other frames as well. This allows identification of this bolt as a larger type.
In this picture, an obviously middle-sized bolt is about to strike the asteroid. These asteroids were at least on the order of 20 meters in diameter. The asteroids appear to be slightly shorter than the diameter of the Millennium Falcon. Several asteroids were also vaporised when in close proximity to the Falcon itself in later scenes by long TL bolts. Since the ISD in pursuit would only have vaporised asteroids that were in its path, these asteroids were much closer to the Falcon than they were to the camera. The size of the Falcon is in despute, but when scaled against an ISD, it must be around 40 meters wide, and slightly longer. In these images, a 35-40 meter diameter estimate seems more…