# Kilojoules to calories



## Creakyknees (Sep 21, 2003)

What's the correct conversion rate? 

I've heard KJ*1.5=calories, but a couple online calculators come out more like KJ*0.25... ?


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## Wookiebiker (Sep 5, 2005)

About 1:1 when taking out the inefficiency of the human body. 

The reality if I remember correctly is it's about 4 calories to 1 kj, but since the human body is only about 25% efficient it comes out to 1:1.


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## overgeared (Mar 22, 2011)

there are about 4.2 joules in a calorie.
the "calories" normally used to describe the energy in food are really kilocalories (thousands of calories), so 100 of those is going to be about 420 kilojoules. 
many people use 4 as a conversion factor.
depending on effort a rider might burn 800 kcalories an hour or about 3200 kjoules. but as the other poster has said we only deliver about 1/4 of the energy we burn as mechanical energy at the pedals, that means 3200 kjoules burned becomes about 800 kjoules of work and that corresponds conveniently with the 800 kcalories of food energy required to achieve it. this last point may or may not be important depending on how the number you're interested in is calculated.


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## kbiker3111 (Nov 7, 2006)

Its 1:0.239 or 4.18:1 kJ to Kcal. 

25% efficiency is at the high end of human efficiency so you're more likely in the 1.2:1 range.


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## B2 (Mar 12, 2002)

Creakyknees said:


> What's the correct conversion rate?
> 
> I've heard KJ*1.5=calories, but a couple online calculators come out more like KJ*0.25... ?


I always thought that it was a little less than 1:1 after a reasonable efficiency rate is taken into account. FWIW Garmin (notoriously inaccurate in the past) calculates calories very consistently with my data at about 0.85 to 0.95 calories per kj.


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## Dream Plus (Feb 4, 2004)

I don't know whether *my* efficiency is 25% or not but as a ballpark figure, the 1:1 ratio of kJ to Calories works OK.



B2 said:


> I always thought that it was a little less than 1:1 after a reasonable efficiency rate is taken into account. FWIW Garmin (notoriously inaccurate in the past) calculates calories very consistently with my data at about 0.85 to 0.95 calories per kj.


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## chase196126 (Jan 4, 2008)

There used to be a KJ to Kcal converter on the Saris website that was designed by Allen Lim. From what I remember the range, depending on efficiency, ranged from 1.15 or 1.2 Kcal per KJ for inefficient people, 1.1 for average, and 1.0 for above average efficiency. 

I personally use 1:1 because it gives me a little built in buffer which can help with weight loss


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