How does Strava calculate calories?

[KneesUp]

I’m not expecting the calories figure on strava to be anything like accurate, especially as I have no sensors, but I’d expect it to be consistent. I’ve done the same commute the last two days with times 18 seconds apart over 2.6 miles, but yesterday it guessed at 254 calories and today it went for 30 calories - which is quite a difference. It’s all downhill, pretty much, if that helps?

 

[PaulSB]

I can't answer your question but a better comparison could be the uphill ride home. You'll be working then whereas on the downhill you may be coasting more at times than you realise.

 

[Heltor Chasca]

I think it’s nonsense. It doesn’t account for panniers, heavy bikes, road surface, weather etc. The other day it calculated I used up 10000 calories on a 10 hour ride 😮

 

[Tenkaykev]

Over the years I've used a general "rule of thumb".

100 kilo calories per mile for running, 50 for walking ( not strolling)

From my perceptions of effort whilst exercising I'd tend towards 50 for cycling ( not caning it) but a steady effort.

I've found it a handy tool for working out my post exercise rehydration strategy. A 10k run = 3 pints of Tanglefoot or equivalent.

 

[Venod]

This any good I haven't read it.

https://support.strava.com/hc/en-us/articles/216917097-Calorie-Calculation

 

[Dogtrousers]

We know how it calculates power
https://support.strava.com/hc/en-us/articles/216917107-How-Strava-Calculates-Power

Power is effectively calories per second. So at a guess they sum the amount of work done in joules based on the above power calculation. Then convert it to a daft unit, calories.

Try comparing the Strava power estimates for the two rides, see if you get a similar disparity.

Edit cross post with @Venod

 

[vickster]

My rule of thumb, 30-40 calories per mile. Less if a lightweight rider, or very easy terrain. More if a heavy rider, and/or tough terrain (uphill a lot)

 

[swansonj]

My rule of thumb, 30-40 calories per mile. Less if a lightweight rider, or very easy terrain. More if a heavy rider, and/or tough terrain (uphill a lot)

Doesn't it depend considerably on how fast you cycle?

 

[vickster]

Doesn't it depend considerably on how fast you cycle?

Ok, you could add effort but speed depends on terrain too? It's a guesstimate like any other calorie calculation done outside a lab!

 

[si_c]

Strava power has calculated for me quite consistently when I've used it, that being said I know it's not accurate.

As a guideline I use about 40 to 50cals per mile, depending on how hilly it is, bearing in mind I weight 95ish kg.

This is backed up by my power meter, but if you ride faster then expect to burn considerably more.

 

[roubaixtuesday]

According to the link "Strava uses your power output and a coefficient for human efficiency. " Checking a recent ride of mine, the coefficient used is about 0.25 ie you burn 4* as many calories as you put out power.

I find the Strava calories pretty consistent and reliable. In essence I think they work by using an aerodynamic coefficient, a constant resistance and a velocity dependent resistance. There's a description of the type of model used for this sort of thing here.

https://ridefar.info/wp-content/uploads/positions.jpg

Strava also takes into account the power gained or lost from gravity, so will subtract (or add) the energy gained or lost in climbing/descending.

254kcal in 2.6 miles sounds like a *lot*, and it's on top of the energy gained from descending so I'm guessing there is some glitch associated with that figure. It equates to 100 calories/mile, which is double what I clocked on a recent hilly ride. Have a look at the analysis. 30 kcal sounds realistic for a downhill 2.6 miles.

On a generally downhill ride, you can expect the figures to fluctuate a lot from ride to ride, because Strava is essentially guessing what your resistance is, and if it's close to your freewheeling speed, a small amount either way will make a big difference to net calories.

 

[Milkfloat]

They do it using one of these.

 

[vickster]

Strava power has calculated for me quite consistently when I've used it, that being said I know it's not accurate.

As a guideline I use about 40 to 50cals per mile, depending on how hilly it is, bearing in mind I weight 95ish kg.

This is backed up by my power meter, but if you ride faster then expect to burn considerably more.

Unless going downhill

 

[swansonj]

Ok, you could add effort but speed depends on terrain too? It's a guesstimate like any other calorie calculation done outside a lab!

Yeah, agreed, it's all approximate.

But when I was commuting before retiring, my morning journey took anything from 32 minutes to 45 minutes, depending partly on traffic but largely on whether I was in a mood to push myself or not. 50% difference in time equates to considerably more than 50% difference in power, and still more than 50% difference in calories per mile, once you're into the speed regime where wind resistance dominates?

 

[PK99]

Doesn't it depend considerably on how fast you cycle?

Per mile, the difference is small - high effort for short time vs low effort for longer time