calorie burn of swimming?

It depends on your weight and the effort you are putting in. As an example, I weight 170 pounds and when I swim for about 30 minutes, I burn roughly 250-300 calories.
I do agree that I often feel quite hungry after swimming, and that hunger is usually outpacing whatever calories I just burned during the workout. For me, I feel less hungry throughout the rest of the day if I quickly eat something fairly high in protein within an hour of my workout. I like skyr, the icelandic yogurt.

I'm certainly no expert and I've wondered the same thing. Most online calculators give about 500-600 cal/hr. Of course there are a ton of factors that affect calorie burn. Doing sets vs continuous swimming will burn a lot more calories, etc. Also, it depends if these calculators are including basal metabolic calories, which is your baseline calorie burn if you were just sitting on the couch. It's important to know if you are including these or not if you are counting total calories.

For example, if you swim one hour and you use a factor of 500 cal/hr, if that includes your BMR then 80 of those calories came from just being alive and 420 came from swimming. This becomes more of a factor in lower calorie burn exercises such as walking or riding slowly on a bike for example, because double counting BMR within the workout and in the background can drastically change your overall calorie burn.

The calorie burn thing is tough because it is so individual. If I don't wear my heart rate monitor and ride 50 miles at 21 mph on my bike my Garmin and MyFitnessPal will show about a 3,700 calorie burn. If I wear my HRM they will then estimate the exact same exercise at around 1,400 calories. So you can see the crazy difference. I have a pretty low HR so I think that accounts for the discrepancy, but it also shows how these estimates are all over the place.

The bottom line, however, is if you are using a set of numbers and assumptions and the result of a caloric deficit results in you losing weight, then you know you're on the right track. If you are counting calories and showing a deficit but staying the same weight or gaining weight (assuming muscle mass is constant) then your calorie burn assumptions need adjusting.

Not sure of the answer but as a long-time swimmer, I can testify that swimming does seem to really stimulate the appetite, probably in many cases out of proportion to the calories burned. For me this is particularly true if the water was cool/cold. I'm guessing that this has to do with body temperature---after a long/hard run or bike, normally your body temp is a bit elevated and this suppresses appetite for a while afterwards; for swimming, that doesn't happen so one is hungry right away. Guessing that calories burned would depend a lot of the intensity of the workout. The low calorie rate is probably for leisurely lap swimming. If you're doing a hard workout, or incorporating high-energy strokes like butterfly, that's going to go up.

All of these responses are very helpful, thanks! I will try to watch more of what I eat after a swim...