I was looking around at Friesian horses and read that the average weight for an adult is about 1300 pounds, which got me to thinking, do any of you base your fursona's weight around that of the actual species or do you just make the weight whatever you want?
There are no dragons I can put on a scale, so I had to do the best that I could based on some simple math. Weight has a direct correlation to volume. So if a creature's volume doubles, its weight should roughly do likewise.
This leads to a simple relation to the creature's relative size:
Weight = (Size) ^3 * Constant
The constant varies based on the creature's shape and how you measure its size. For humans, size is best measured by height. If you take a 5'9" (1.75m) adult who weights 187 pounds (85kg), that constant will be 15.86. Using that number, if you shrink him proportionately to 3'3" (1m), he'll weigh 35 pounds (15.86kg.) My son weighed about that when he was 3 feet tall, so the formula works.
For dragons, I looked at theropods. (Think T-Rex.) Theropods are usually measured by length from snout to the tip of the tail, and are roughly dragon-like in shape. Looking at various species, I found a value for that constant that ranges from 3-6. Since dragons are a bit beefier (having thicker forearms and wings) and because Telnac's made mostly of carbon with some heavier parts such as steel, not mostly water, I chose a slightly higher value for him: 7.
Telnac is 9 meters in length (30 feet.) Using the above formula & a constant of 7 places his weight at 5,103kg (11,226 pounds.)