# Calories vs. Kilojoules



## steve_e_f (Sep 8, 2003)

Quick question:

My Garmin reports 1150 calories burned on a ride. Golden Cheetah computes 1445 Kilojoules.

The Time Crunched book says Kilojoules are approx 1 to 1 with calories (but admits that its not exact).

Is the discrepancy between Garmin and Golden Cheetah normal? Which is more reliable?

gracias.

-sf


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## MontyCrisco (Sep 21, 2008)

Deleted post... Sorry - my bad - shoulda read the OP more carefully.


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## steve_e_f (Sep 8, 2003)

I'm not sure I follow.
I am trying to use wattage to calculate calories...

On this workout for instance:
http://connect.garmin.com/activity/22890183
Garmin Connect says 1163 calories.
Golden Cheetah says 1453 kilojoules 

I thought there was approximately a 1 to 1 for calories vs kilojoules (according to the Time Crunched book), but those numbers are nowhere close, so is Garmin wrong or within the margin of error, or am I very confused overall (which is very possible).

I'm just trying to decide if I can have ice cream for desert or not.


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## stevesbike (Jun 3, 2002)

all systems estimate calories: To convert kilojoules to calories, divide the number of kilojoules by 4.184. The estimation comes in re how efficiently your body does this. Most put this at around 25%, so you need to multiply by 4 to estimate - hence, 1 kilojoule = 1 calories (given an estimate of efficiency).


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## Poncharelli (May 7, 2006)

I understood that powermeters capture the *mechanical* energy you put out. But it does not capture the *heat loss* energy from your body. 4.184 kilojoule = 1 food calories. But since 3/4 of your energy is heat losses, then you can say that 1 kilojoule = 1 calorie, for all practical purposes. (The logic is something like this, I may be wrong). 

So powermeter calories burned is just an estimate. There would probably be situation where you would release more heat calories from your body (long climb on a real hot day), and it wouldn't be compensated. 


But the error between your two devices seems reasonable, considering their inherent inaccuracy. I think I would trust the powermeter more though.


But in either case and regardless of measurement of device (even if it's putting you and bicycle in a calorie chamber), I would most definitely still have the ice cream. .


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## boon (Dec 14, 2005)

Garmin's calories calculation is known to be unreliable.


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## thoran (Aug 1, 2009)

Poncharelli said:


> I understood that powermeters capture the *mechanical* energy you put out. But it does not capture the *heat* energy loss. 4.184 kilojoule = 1 food calories. But since 3/4 of your energy is heat losses, then you can say that 1 kilojoule = 1 calorie, for all practical purposes. (The logic is something like this, I may be wrong).


It doesn't really make sense to say 1 kilojoule = 1 Calorie. 1 calorie = 4.18 joules (or 1 Calorie = 4.18 kilojoules naturally) no matter how you slice it. If the Garmin says 1150 Calories and the Golden Cheetah says 1445 kilojoules, then it sounds to me like Golden Cheetah is giving you the actual energy your body output at the wheel during the ride and the Garmin software is giving you a calculated amount of energy (using the energy output at the wheel) based on some assumed efficiency of your body.


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## Marc (Jan 23, 2005)

boon said:


> Garmin's calories calculation is known to be unreliable.


I wouldn't say "unreliable" so much as "Completely Wrong", or perhaps "Your ouija board is closer to actual value".


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## Kerry Irons (Feb 25, 2002)

*Not understanding*



thoran said:


> It doesn't really make sense to say 1 kilojoule = 1 Calorie. 1 calorie = 4.18 joules (or 1 Calorie = 4.18 kilojoules naturally) no matter how you slice it. If the Garmin says 1150 Calories and the Golden Cheetah says 1445 kilojoules, then it sounds to me like Golden Cheetah is giving you the actual energy your body output at the wheel during the ride and the Garmin software is giving you a calculated amount of energy (using the energy output at the wheel) based on some assumed efficiency of your body.


You have it backwards. The difference is exactly as others have described: because the human body is around 24% efficient (fit athlete), a kilojoule is about a (food) calorie. Here are some numbers for your undersanding: 200 watts for an hour is 720 kj. 200 watts for an hour (assuming 24% efficiency) is 715 calories.


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## Kerry Irons (Feb 25, 2002)

*Another way to think about it*



Marc said:


> I wouldn't say "unreliable" so much as "Completely Wrong", or perhaps "Your ouija board is closer to actual value".


How about "Magic 8 Ball Says:"


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## thoran (Aug 1, 2009)

Kerry Irons said:


> You have it backwards. The difference is exactly as others have described: because the human body is around 24% efficient (fit athlete), a kilojoule is about a (food) calorie. Here are some numbers for your undersanding: 200 watts for an hour is 720 kj. 200 watts for an hour (assuming 24% efficiency) is 715 calories.



This is really an argument about semantics and units. Both kilojoules and Calories are units of energy plain and simple. There is no reason that we should assume that a kilojoule means energy output at the wheel but that a Calorie somehow includes a presumed body efficiency. In fact, many countries do not use the Calorie as a unit of measurement and nutrition labels on food give values in kilojoules.

Again, the issue really is that one piece of software is giving an actual energy output measured and the other is using that same energy output and giving an estimated amount of energy consumed by your body. The units are just clouding the issue. We're making the issue worse by including the term "food calorie" which is really the same as the kilocalorie or Calorie.


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## Marc (Jan 23, 2005)

Kerry Irons said:


> How about "Magic 8 Ball Says:"


Do they make carbon fiber dartboards with ceramic bearings?


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## carlosflanders (Nov 23, 2008)

I've compared my Garmin Calories to powertap #s many times. 

If it's hilly or windy then PT kJ is about 60--65% of Garmin's cals.

If it's a flat ride (i.e. Midwest) then measured PT kJ are about 70% of Garmin's cals.

No idea how GC computes its values.


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## steve_e_f (Sep 8, 2003)

Poncharelli said:


> But in either case and regardless of measurement of device (even if it's putting you and bicycle in a calorie chamber), I would most definitely still have the ice cream. .


bingo. there is the info I needed. thanks!

and thanks all for clearing it up sorta... and complicating it a little... but at least being an interesting read.


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## Doc_D (Mar 16, 2006)

I also agree that the Garmin calorie's burned estimate is garbage (I still love my garmin though!). 

As many others have said here, when a human's efficiency is taken into account 1 kilojoule of work done at the rear tire is roughly equivilent to 1 calorie (technically kilocalorie) burned by the human body.

For a 1 hour ride my Garmin might report 800 calories burned but my powertap would show about 405 kilojoules of work done at the rear tire. So for me, the Gamin is overestimating calories burned by roughly 100%.


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## the mayor (Jul 8, 2004)

Do you really need software to tell you to eat ice cream?


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