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# Calories to Watts

I have a trainer this winter that measures watts, but, last riding season I had a Polar HRM, and no way of knowing watt output for recorded rides. All I have is the calories used, time, dist, HR, ect. I have found the formula to convert watts to KCalorie, but not KCalorie to watts. Is it possible ? I would like to have some idea of power output from this past season, to get an idea of where to improve next.

### Re: Calories to Watts

Quote:
 Originally Posted by jp111 I have a trainer this winter that measures watts, but, last riding season I had a Polar HRM, and no way of knowing watt output for recorded rides. All I have is the calories used, time, dist, HR, ect. I have found the formula to convert watts to KCalorie, but not KCalorie to watts. Is it possible ? I would like to have some idea of power output from this past season, to get an idea of where to improve next.
Watts is power, KCals is energy. You either have to convert Kcals to watts-hour:

1 KCal = 1.163 watt-hour

or Watts to KCal/hour or any other power=energy/time.

Try:
for a nice freebie units converter.

### Re: Calories to Watts

Quote:
 Originally Posted by jp111 I have a trainer this winter that measures watts, but, last riding season I had a Polar HRM, and no way of knowing watt output for recorded rides. All I have is the calories used, time, dist, HR, ect. I have found the formula to convert watts to KCalorie, but not KCalorie to watts. Is it possible ? I would like to have some idea of power output from this past season, to get an idea of where to improve next.
as a ball-park estimation you can directly convert kcal to kj on a 1:1 ratio (i.e., 500 kcal = 500 kj) for when you want to convert kcal to watts -- this is because although there is 4.18 kcal to 1 kj humans are around 20 - 25% efficient when cycling (so vaguely everything cancels out).

In other words if you *accurately* knew that you'd expended (e.g.) 500 kcal and ridden for (e.g.) 1-hr then you'd have averaged 139 W = (500 kcal / 3600 secs) * 1000.

However, given that the Polar can only estimate energy expenditure based on HR, it isn't accurate (or else power meters would be a waste of money). and given that you're using a trainer (and not a power meter) i'd say that you can't make any comparisons about power and/or energy expenditure -- due to the inaccuracies of all the equipment you're using

ric

### Re: Calories to Watts

Quote:
 Originally Posted by ric_stern/RST as a ball-park estimation you can directly convert kcal to kj on a 1:1 ratio (i.e., 500 kcal = 500 kj) for when you want to convert kcal to watts -- this is because although there is 4.18 kcal to 1 kj humans are around 20 - 25% efficient when cycling (so vaguely everything cancels out). In other words if you *accurately* knew that you'd expended (e.g.) 500 kcal and ridden for (e.g.) 1-hr then you'd have averaged 139 W = (500 kcal / 3600 secs) * 1000. However, given that the Polar can only estimate energy expenditure based on HR, it isn't accurate (or else power meters would be a waste of money). and given that you're using a trainer (and not a power meter) i'd say that you can't make any comparisons about power and/or energy expenditure -- due to the inaccuracies of all the equipment you're using ric
On occaision, at work I use an excercycle-( I can't remember the brand at the moment) it gives calories per hour and calories burned. Is this really Kcals not calories? - Usualy on a mid level resistence you get ~ 1,000 calories/hour.

### Re: Calories to Watts

Quote:
 Originally Posted by Perro Loco On occaision, at work I use an excercycle-( I can't remember the brand at the moment) it gives calories per hour and calories burned. Is this really Kcals not calories? - Usualy on a mid level resistence you get ~ 1,000 calories/hour.
i'd assume that it meant kcal. however, 1000 kcal/hr = ~ 278 W -- that's quite a hard effort (that's about 42 km/hr for me during a TT).

ric

### Re: Calories to Watts

Quote:
 Originally Posted by ric_stern/RST i'd assume that it meant kcal. however, 1000 kcal/hr = ~ 278 W -- that's quite a hard effort (that's about 42 km/hr for me during a TT). ric
I can only do it for about 20 minutes. I doubt it is super accurate. I am currently not in great cycling shape (work has been prohibitive for the last several months-recently moved settling in.....) but have started back again.
The other night I was able to maintain ~ 28 Km/ hour into a headwind on a flat for ~ 15- 20 minutes before sensibility took over. me and bike weigh about 90 kg (yeah, I know need to drop some weight, get rid of that steel frame...) so it might not be way off.

### Re: Calories to Watts

Quote:
 Originally Posted by Perro Loco I can only do it for about 20 minutes. I doubt it is super accurate. I am currently not in great cycling shape (work has been prohibitive for the last several months-recently moved settling in.....) but have started back again. The other night I was able to maintain ~ 28 Km/ hour into a headwind on a flat for ~ 15- 20 minutes before sensibility took over. me and bike weigh about 90 kg (yeah, I know need to drop some weight, get rid of that steel frame...) so it might not be way off.
sounds like it's way off. keep up the good work though and you'll be cycling faster and for longer

ric

### Re: Calories to Watts

Quote:
 Originally Posted by ric_stern/RST sounds like it's way off. keep up the good work though and you'll be cycling faster and for longer ric
Thanks, typo on my last sentence-I agree I thought it was way off.

Ric,