Why Strava distance is always 0.01 mile shorter than Garmin distance?

[Silentvoyager]

I know it is a small thing but it is one of those things that is quite annoying about Strava. You know that situation when you finish a run and notice that it is very close to a round number of miles, than you run a bit further to make it e. g. 5 miles. Then it uploads to Strava and shows as 4.99 miles in some parts of the app and 4.9 miles in other parts of the app (e. g. the training calendar). Can Strava stop doing that? 

[Silentvoyager]

This keeps coming up in social networks regularly. There are always a lot of misconceptions about what everyone refers to as "Strava tax", but I think at the end that simply harms reputation of Strava. It would be better for Strava to stop being stubborn about this issue and make distances match to Garmin and other brands by doing proper rounding.

https://www.reddit.com/r/Strava/comments/128fzjh/why_does_strava_apply_a_penalty_of_10m_to_every/?ut...

[MattS_bsb]

This also comes up in group runs where there's a goal distance (say 10 miles), and when folks are approaching the end of the run/distance, I'll usually remind folks to "round up for STRAVA!!".  We've all endured that slight sting of seeing our final distance show up as .99.  Oh by the way, I've seen STRAVA tax become a real thing for myself and others using indoor rowers (no GPS), usually around 3 meters.  Weird right?

[Silentvoyager]

I wanted to add two more points to this thread.

1) Strava's rounding down of the distance is well known and disliked on Reddit (e.g. r/running subreddit), and often mentioned and referred to as "Strava Tax". If nobody likes that, why Strava insists on doing that? 

2) The same rounding down seems to apply to elevation gain. 

[CreakyCrank]

@Silentvoyager To your first point, I believe what @varun is saying in the response when they refer to "the care we aspire to take with data correctness and integrity. " is that Strava is not going to round up, because they are more concerned with data correctness and integrity, or "running all the way to the line".  - basically, they (Strava) are ensuring that you go the full distance, and not rounding up ensures this... you have to 'cross that virtual finish line'.

Elevation would also apply (but this is even more of a contentious issue, and your elevation will vary wildly from device to device).  I don't count on any device to be accurate with elevation numbers - I can ride next to others and have a variation in elevation between us of 100s of feet (or meters/metres if you prefer metric)... I can complain all day about elevation! (but it really has nothing to do with Strava when the GPS devices are so varied in the numbers it gives).

I know the "Strava Tax" can be frustrating/upsetting, and can cause an athlete to not get a completion of a certain distance, but I don't think Strava will start rounding up anytime in the near future... my best advice is to run/ride a bit further than the distance you are looking to achieve, or climb a little bit higher (also, this is likely not the answer you are looking for, but it is the only solution based on @varun's response on Strava's methodology). 

[Silentvoyager]

@CreakyCrank , I understand @varun's answer - there is no need to explain it to me.

My point is that every other GPS device brand does proper rounding. And then Strava says - we know better and we better not award you those extra 0.005 miles (which is about 10 steps) in case you haven't actually run that. By doing that Strava says that it knows better than any other other GPS device brand, which is pretty ignorant.

The points is that it isn't scientifically correct and only causes annoyance for the following two reasons:

1) The GPS distance accuracy is 0.5-1% at best and can easily be up to 5% wrong on a challenging terrain (that is my personal experience), and even worse than that. So if someone has run 5 miles, in reality that may be anything between 5.95 and 5.05 miles in the best case. So always rounding down in that situation in case they didn't run that extra 0.005 miles is simply not scientifically correct. It just introduces a bias for no particular reason.

2) @varun mentioned that GPS devices tend to measure GPS distance long. But that is simply not correct. Perhaps that was the case 10 years ago. It is true that early GPS devices that relied on GPS only had quite a bit of wobbling which could add to the distance. But modern devices use sensor fusion and tend to factor accelerometer and gyroscope heavily in the distance calculation and counteract the wobbling.  If anything, modern devices tend to oversmooth the track, especially around turns, and the distance tends to be too short, especially when running on trails with a lot of turns. If you don't believe me, try searching for Garmin Forums  for "distance short": https://forums.garmin.com/search?q=distance%20short

When I know that my Garmin device already under-measures the distance and then Strava reliably subtracts 0.01 miles from that, that causes nothing but irritation. 

And just to make it clear, I am not saying Strava should round up. It should do proper scientific rounding instead of truncation that it currently does.

[varun · Accepted solution]

Hi @Silentvoyager, 

We know this has been a long-time quirk, and often a frustration for many athletes, including some of our own employees! The reason this happens is that Garmin (both the device and Garmin Connect) rounds up distances, whereas Strava rounds down. Distances are always stored in meters on devices and then shown on Strava in the athlete's preferred units (i.e. miles/yards for imperial and kilometers/meters for metric). So for example, a distance that comes over in a file as 4995 meters will get displayed on Strava as 4.99 km and on Garmin as 5.00 km. Similarly, if on your watch you run until you see 1.00 miles, that might actually be something like 1608.0 meters (0.9994 miles) and Strava will show 0.99 miles.

It is also worth clarifying that most Garmins, even relatively older ones, provide a distance directly in the file that Strava uses. There are cases we calculate distance ourselves from the raw GPS points; for example, if a certain device doesn't provide it. And athletes can also choose to use our calculated distance to override the device one - see How Distance is Calculated for more. 

One other nuance for the question from @MattS_bsb regarding race distances like a half marathon or marathon. There are features like Best Efforts and Challenges based on those Best Efforts that require athletes to complete a certain distance. One thing we have seen is athletes who run 26.2 miles and not receiving credit. This stems from the same issue above - that a marathon is 26.22 miles when converted from its official distance (26 miles and 385 yards), and athletes are often slightly short.

We understand that this is a bit of a philosophical stance we've taken - the digital version of "running all the way to the line". There is a tradeoff here between the consistency with Garmin and satisfaction of the round numbers (because yes, we've all been there), and the care we aspire to take with data correctness and integrity. This is one of an exceedingly long list of nuances around data as we pursue making Strava work for thousands of devices, each with its recording subtleties and differences.

Hopefully that helps clear things up and explains why you might see some crafty athletes running til they see 1.01 on the watch. We will strive to continue using this forum as a place to transparently explain more of these types of situations to athletes.

[Smarties]

Your philosophical stance just cost me a pb on a half marathon that i have been training for for 5 months. Garmin says 21.1km and Strava says 21.09km. What gives you the right to do this? Rounding down is just stupid. I work with data for a living and no dataset is 100% correct anyway, but you are denying athletes pb’s for a couple of meters. I trained, i cried, I covered the distance but yet you deny me a pb. Do you really think that anyone cares about your philosophical stance? Its stupid. Who is the clown making these decisions in your company? Get your act together Strava!

[Silentvoyager]

Yeah, the true half marathon distance is 21.0975 km. You were probably just a few meters short. I think Strava's stance about this issue doesn't show them in a good way. I remember seeing a comment from Strava that all GPS devices always measure distance long, which is clearly not the way with modern GPS devices if you read Garmin forums. The Sony chipset is especially bad in that regard. Distance measurement does no longer come directly from GPS. It comes from fusing data between the GPS and the accelerometer, and in my experience Garmin's distances often ends up being a bit on the short side when running on open terrain and even more short when running on trails. 

I think the right solution would be (a) to round exactly the same way as Garmin and (b) award a PB even when the distance is a bit short. How much, I don't know but something like 99.5% of the distance sounds like the right threshold. That would significantly reduce disappointment of users when they don't get a well deserved PB due to being a few meters short. 

[Smarties]

So if your sales director has a sales target of say $10k and that person only reaches $9,999.99, would you deny him his bonus ? I dont think so. Match Garmin or dont sync with Garmin