Lets just say as a hypothetical average over an hour period, which one burns the most calories? (By average, averaging all types of endurance, VO2 and speed workouts.)
It seems like the run should burn the most, but the only time I am extremely hungry is after swimming, so I am curious what others think or know to help better fuel on training days. Last time I trained for an IM I lost 15 pounds, so I obviously miscalculated for months. I’d like to not do that again.
For myself when calorie counting I’ve found that a normal 1 hour swim session burns about 300-400 calories
A moderate 1 hour ride burns about 400-500 calories
A moderate 1 hour run burns about 600 calories
.
https://www.omnicalculator.com/sports/calories-burned
Enter your weight, duration, and activity and it calculates it.
I use this for yearly calorie burn for all my activities. This allows me to adjust my weight and speed year-to-year as a more accurate judge of expenditure.
I used to average 19.7mph on the bike, now I’m in more 18.8mph. In my IM years I weighed 165-ish now I’m 180-ish. Biking the same distance at the new weight and time is 20% more calories burned by that calculator.
I’m not qualified to answer this, but did overhear a 10min back and forth in a bike shop one day about this between an old school bike racer from the 70’s and a current day triathlete.
I think the time period matters. Like, are we talking an hour or something like an ultra ultra run or audax bike or channel swim?
I agreed with the triathlete at that moment that it should probably be the swim for an hour if you could somehow accurately track it like you can with a bike. I don’t know, my rationale was you’re using legs and arms and whole body.
Interested to hear what others say.
I’ve got no idea what the “right” answer is but I do know that I am always at my leanest when I’m swimming consistently (5-7x per week). Since I haven’t swam since 2014, I’m not that lean at the moment. 
I believe swimming allows for the highest average workload of all three sports. Running you can match swimming, but not as often. The easiest swim pace will be way more energy use than easy run and easy bike.
So on average per hour, swimming will burn the most. But the hard hours of bike or run, will match swim in my estimation. Its just that if I do 10 hrs or swim, 10 hrs of run or 10 hrs of bike, I will burn the most on the 10 hrs of swimming
When I was at the peak of my tri training, I figured that the only way I could normalize my overall training volume was to convert each into calories and track that value. It allowed me to have emphasis weeks in the different disciplines and still maintain my training load.
I honestly don’t remember all the conversion values, but do remember that a mile run (at about a 7:30 pace) equated to 117 cal/mile, and riding at 18 mph equated to 49 cal/mile. Don’t remember the swimming conversion.
BUT… and here’s the thing, it’s going to depend a lot on pace/speed. Not so much WHILE you’re doing it, but the long taper back to basal rate afterwards. And as I remember, while swimming is very calorie intensive DURING the activity, running had the longest taper interval, and thus the highest caloric impact overall.
running wins hands down because of the impact, which causes more muscle fiber/bone damage that needs repair. A calorie is not really a calorie in the human body. lots of biochemical processes that determine composition
this is my understanding, as well
including recovery, running will require the use of the most cals…
Run, but that post-swim hunger is a common phenomenon.
Your estimate about a moderate bike ride seems low. When I ride the Peloton, a reasonably hard workout for an hour will burn over 900 calories. The Peloton profile takes into account sex, height, weight and age when estimating the calorie burn. I realize it is not exact, but I believe it is fairly close when comparing to my Wahoo Elemnt.
running wins hands down because of the impact, which causes more muscle fiber/bone damage that needs repair. A calorie is not really a calorie in the human body. lots of biochemical processes that determine composition
I think this would depend on the proficiency of an individuals for swimming. In general, the overall recovery for most triathletes will be longer for running than swimming, because their average swim effort is so low, but for a proficient swimmer, lots of calories will continue to burn long after the workout is done due to the effort level while in the water. But you are generally likely correct for the overall impact on the day, not just the workout where an average swim will use up more energy than average run. This is why most people can’t do 3 hrs swims (they get completely glycogen depleted in barely 90 min) , but almost everyone with a bit of training can do 3 hrs runs.
But after workout is over, that makes sense.
It depends on intensity.
Same aerobic intensity, same calorie utilization.
Your estimate about a moderate bike ride seems low. When I ride the Peloton, a reasonably hard workout for an hour will burn over 900 calories. The Peloton profile takes into account sex, height, weight and age when estimating the calorie burn. I realize it is not exact, but I believe it is fairly close when comparing to my Wahoo Elemnt.
I bet you burn more calories on the Peloton or ANY indoor ride than outdoors. There is no stopping, no drafting, no downhills to freewheel. Thus indoor tends to always use more energy
Your estimate about a moderate bike ride seems low. When I ride the Peloton, a reasonably hard workout for an hour will burn over 900 calories. The Peloton profile takes into account sex, height, weight and age when estimating the calorie burn. I realize it is not exact, but I believe it is fairly close when comparing to my Wahoo Elemnt.
That’s probably because most people are bigger than me at 65 KG and 160 cm
A moderate ride of 20 mph is 130 to 140 watts
140 watts = 504 kJ/hour ~ 500 calories burned by me
Edit: I also calculate about 85 calorie per mile of running
Ai_1 sorry to mix units 
That makes sense. I did not take into account the difference in size. I am 5’11" and 175 lbs. So I would burn more calories during an hour ride. I typically average around 200 watts in an hour Peloton power zone workout. The bike tracks kilojoules as well as calories.
Edit: I also calculate about 85 calorie per mile of running
Running burns/uses 0.6 KCal/lb/mi.
A 100 lb person will burn 60 KCal per mile run
A 200 lb person will burn 120 KCal per mile run
etc.
A 200 lb person running 6:00 miles for 1 hour burns 1200 KCal
Swimming can burn the same.
Biking can burn the same.
Biking will win out for grand total unless you are out doing 6 hour ultra runs or swimming from Key West to Cuba
On a per-minute basis, assuming roughly comparable intensities, running is the winner here. But if the question is reframed as during a typical training week or training block, which of the three burns the most total calories, I would guess it’s cycling due to it eating up the most training hours out of the three disciplines, typically.
This is my month of April so far according to Apple Watch. I’m a decent runner, average cyclist, poor swimmer.
Swim: 1:30 hours, 1,004 calories, 11.2 cal/min
Bike: 19:28 hours, 13,852 calories, 11.9 cal/min
Run: 12:10 hours, 10,045 calories, 13.8 cal/min
There’s also the factor that cycling has “breaks”, e.g. must of us aren’t pedaling full-tilt down descents (at least I’m not). If you pedal exclusively on trainers then maybe cycling would be closer to running.
Most of the ex phys texts have running around 100cal/mile last I checked. If you’re going faster you’re burning more per minute but also getting done sooner. Uphill increases that a bit downhill decreases that a bit.
For those of you looking at calories when riding a better thing to look at is actual work done which would be kilojoules (kJ) which can then be converted to calories burned. Most of the calorie guesstimators such as garmin, wahoo etc are just that, guesstimates.
Most of them are consistently off and in my athlete cohort when compared to kJ it’s in the 20-60% range, which is a HUGE range.
Like most people have said, running appears to, assuming intensity and time are roughly consistent. BUT a lot of the calculators don’t take water temperature into account, and the calories burned keeping your body around 98 degrees when you’re swimming.
Can’t remember where I saw it, and it may have been pseudoscience, but there was an interesting article about how you burn fewer calories during the actual swim workout, but quite a bit more while your body actively works to keep warm in cool water. That always made sense to me - it does explain that “so hungry after swimming” phenomenon.