If you’re not a powermeter user, Strava will give you an “estimated power” number for your ride and also for all the segment data. This power number is “calculated” by Strava using road gradient, speed, and rider info such as weight (plus some other fancy physics calculations I’m sure).
On my recent trip to Melbourne, I left my powermeter pedals at home, opting instead to take a regular set for the rental bike. I’ve been riding with a powermeter for several years now, so I have a good handle on what numbers I can lay down over different time frames, plus what certain power levels feel like. So instead of seeing my real power data after the ride, I got to view Strava’s estimates.
Let’s take this Melbourne ride as a comparison…
According to Strava’s algorithms I averaged 343 watts for this three hour ride.
From many years worth of rides in the legs, I can confirm that Strava’s estimated power data ranges from “somewhat accurate” to “wildly ridiculous” (and everything in between). In terms of using it for training purposes, it’s next to useless. Actually, beyond useless.
I can tell you without a shadow of a doubt that I did NOT average anything near 300 watts while tearing it up and down the Beach Road. Not. Even. Close. I’d put it around the 180 watt mark. Needless to say, that’s quite the difference. I’m sure my rental Pinarello didn’t magically give me an extra 100+ watts.
Looking closer, there’s also my PR on the “Black Rock to North Rd” segment. I clocked this one at 35km/hr which gave me a Strava power value of 422 watts for over 15 minutes! BOOM! But let’s be honest here, in reality I can hold 400 watts for all of about thirty seconds…
So why the massive discrepency?!?!
Strava doesn’t know how aero you are, or how fast the road surface was, whether there was a headwind, whether you were hiding in a bunch, or if you got a cheeky draft from a truck, or about a hundred other variables! All of these and more will change the amount of power you need to keep moving forward. Just a change in road surface can be worth 20+ watts.
In certain circumstances, the Strava estimated power data can be quite close. On longer, steeper climbs the numbers look more similar. This is down to variables such as wind and drafting being removed somewhat. The more you sway the calculation towards pure watts per kg, the more accurate the
Strava power data seems to be.
If you’re training, and want to use power, then get a powermeter. I can highly recommend the Faverro Assioma Duo pedal based system. Using the Strava estimates for training will get you nowhere. There are far too many variables outside of Strava’s knowledge. As an interesting metric to look at from time to time, the estimates are totally fine.
Just don’t take “Strava watts” as any form of gospel.
Tempo Cyclist - Tasmania 
That’s really interesting, your numbers. Ours are actually quite accurate, within 15 watts according to a local pro. The fastest we’ve ever done on a Tuesday Night, 29 miles at a 24.1-mph avg, Strava gave me an average of 251 watts. Right where it should have been. 🤷🏻♂️
LikeLike
I have the same Assioma Duo, and so far, I’m loving it. I have Garmin Vector 3 on my other bike, which uses DL1/3N battery, which is extremely hard to find (they are not rechargeable batteries). And I agree … estimated power is not the way to track your training.
LikeLiked by 1 person
They’re a great choice. You hear very few reports of people having issues with them. That reminds me, I need to update the firmware!
LikeLiked by 1 person
Strava even shows watt with mode ‘e-bike’. What’s behind that ? Do you know whether there’s a difference in watt calculation between modes ‘mountainbike’ and ‘e-bike’ ?
LikeLike
I don’t know for certain, but my educated guess would be that there’s no difference in the calculations. Strava likely simply calculates watts based on speed, gradient, and your personal metrics (weight, etc).
LikeLike