Hi FinnYDing, the metric is called "Training Load" in Strava and it is calculated similarly to the TSS. The difference is, that it's using the Weighted Average Watts instead of the Normalized Power. The Weighted Average Watts are again similar to the Normalized Power but mostly slightly lower due to more smoothing.

Thx Jan - I’m aware of that Strava has another measure but wasn’t aware of how it was calculated. 
it would nevertheless be nice to have a TSS calculation in Strava as well to be able to use the same measure across platforms. 
Finn

Hi @FinnYding 

Thanks for posting about this.  We calculate the Training Load by comparing your power during your ride to your FTP and determining how much load you put on your body during the workout. Training Load is a great way to determine how much rest you need after your workouts.

Thanks @Jane11 - that could work out fine if I was only using Strave. But I would like to use TSS as this is - in my opinion - a more common term and thus comparable across platforms.
Do you have any knowledge about the Strava TSS calculator I mention? Is this a Strava recognized tool?

BR

Finn

Hi, 

I know this answers is a bit late, but the TSS Calculater you found is a external tool that calculates the TSS based on your training data from Strava. At the moment you need a PowerMeeter to get correct data. Try it out, you can at any moment revoke the aplications access to your stava data.