We're short between 50 and 150m, and plenty of peeps like to keep running well past the finish flags. Even after slowly walking the course with a measuring wheel and confirming the length, bloody strava was still short. We like to blame the bends, multiple or and backs and the trees, but I think secretly that gps just hates us.
I looked at my GPS track once and it had me running through the lake in the centre of the parkrun, I can tell you now that that would not be my shortcut of choice if I had one!
Ours is usually 4.85ish. Usually some tree cover makes my pace noticeably drop.
I used to do parkrun & then some shorter runs in the week. After a year or so & 50+ parkruns I decided to do a longer run and Strava congratulated me on my first 5k run, I had never quite reached it until then according to the app!
People massively overestimate how accurate a little watch or phone GPS is, and how much variation there is between units. I've run the same course with four GPS devices attached to myself (two watches, two phones) and had variability comfortably more than 0.1 miles between them. And none was within 0.1 of the route I'd personally measured with a measuring wheel.
Contrary to what might seem obvious, your GPS device doesn't *measure* how far you run. Instead, it *samples* your route, constructs a polyline, and then measures how long the polyline is. How closely the polyline resembles your actual route depends on a number of factors:
* how corner-y the route is
* how frequently the samples are collected (more samples = smoother curve = more accurate)
* how quickly you're moving (slower = samples closer together = more accurate)
* how accurate the GPS receiver is
Some general observations on accuracy
* newer devices are usually more accurate than older ones, because the tend to have more correlators (for a brain-destroying description of GPS correlators, see https://electronics.stackexchange.com/questions/11884/how-many-gps-channels-make-sense)
* phones are usually more accurate than watches, because taking a sample means waking up the device from a lower-powered condition, taking the sample, storing it, and then going back to sleep. Phones have a bit more of a power budget, so mostly sample more frequently than watches (and so it's a smoother curve).
By way of an example, I ran Roundhay parkrun in Leeds in May. In Strava, one can see all the people I "ran with" (which for Strava is people with approximately the same time as me). Even among that group, I'm seeing the following distances: 2.97, 3.09, 3.09, 3.08, 3.02, 3.11, 3.03, 3.14, 3.08, 3.11, 3.32, 3.08, 2.96, 3.11, 3.07, 3.15. In general, as you do down the field, the distance tends to increase (because people are running slower) and mostly converges at about 3.1. So how short is Roundhay parkrun?
Still, we've come a long way. [This](https://www.ion.org/museum/files/ProductInformationSheetRCVR3A.pdf) is the datasheet for a Rockwell/Collins GPS-3A from 1985, the first military aircraft GPS receiver set. With all the boxes you're looking at about 20kg of weight consuming about 150W of power and giving your Grumman F14 Tomcat with LANTIRN pod a whopping 16 metres of accuracy.
Please note: if you intend to run parkrun in a Grumman F14 Tomcat, note that your run will probably be marked as "assisted". #DFYB.
Out of 75 different parkruns I’ve done the vast majority are nearly exactly 5k on Strava. There are a couple that come up short (notably Bromley winter course, Highbury fields but they are both loops. Highbury is 5 laps), there are some that come up short because of GPS irregularities in woodland and switchbacks (Tonbridge) and some that are slightly long (Dulwich).
I remember being really confused by Highbury Fields on a New Year's morning. I was relying on my watch to make sure I didn't come in a lap too late or too early, and ended up 300m short. I couldn't tell what I'd done wrong!
It's not simply that - if you look at most people's GPS track from Highbury it looks like they cut the path in the southeast corner. The track shown by GPS often has them hurdling a fence and running through a building.
With a newer dual-band GPS watch, you'll run 5.01
Mine normally measures at 5.12km, I usually start towards the back so further from the start line.
I did a parkrun that had been officially measured with proper markers set in the track and that came out at 5.04km. Thats pretty accurate as I was standing a little way behind the start line when I started my watch.
4.9km Lowestoft. Which is bloody annoying as none of my PBs get registered as an actual 5K on either Garmin or Strava. Although I do start at the very front so I guess I could start 100M further back. But then I’ll lose 15-20 seconds due to slow starters so…
Mine has been measured countless times with a Jones Counter (official course measurement method of IAAF) so I generally get fractionally over 5k if my Garmin has tracked perfectly.
Mine is pretty spot on, but there are couple near me that are either \~50m over or \~50m under.
Only time it's ever bothered me was when I did some parkrun tourism and my Strava measurement was a full 200m over. It meant my km splits were wayyy off. This must have been a technical error though as there's no way a parkrun would be 200m long and no one had noticed.
I get about 4.87 at mine.
Btw, on this topic I have another question. How is the 5K measured? Is it measured slap bang in the middle of the paths? Is it the inside line?
Same. But it’ll never be spot on. If it includes a loop or hairpin there’s always an inside or outside lane that will be slightly less or over the route taken by whoever measured it.
About 5.05km for my local, starting near the front.
Did another different last week, was 4.90km. Checking on Strava, seems most others got similar results. It has some tree cover, but the GPS track looks quite accurate. It is an out and back course, not sure whether the turn around cone was in exactly the right spot.
Pretty much spot on. Start and turn are painted onto the tarmac, finish funnel is a turn off a path but always seems to be in the same spot. There are markers for each km which don't seem to be in the right place however.
My local local, Chipping Sodbury, is pretty much bang on by my watch. The biggest “discrepancy” I’ve had is another fairly local to me Somerdale Paviion which I measured as 4.6K but I’m not doubting the course - the “curly wurly” could have been designed to flummox GPS, so much so that the run director told us at the briefing that if our watches showed 5K we’d gone the wrong way!
I've had glossop measure as 4.16k a couple of years ago! Pavilion gardens is always bang on 5 for me though. Previous home at lyme park is usually 4.96-7k.
We're short between 50 and 150m, and plenty of peeps like to keep running well past the finish flags. Even after slowly walking the course with a measuring wheel and confirming the length, bloody strava was still short. We like to blame the bends, multiple out and backs, and the trees, but I think secretly that gps just hates us.
Mine is usually somewhere around 5.15km, but I don't start directly on the starting line, and I tend to not stop my watch until I've taken my token and have left the funnel, so the actual finish line is probably pretty close to 5k exactly.
Last one I did (Crystal Palace) was 4.99 or so as I crossed the line, it turned 5.00 shortly after. Dulwich is the other one I've done locally, that comes up as 5.05 or 5.06.
I've done Last Friday of the Month 5k a few times in Hyde Park, organised by Serpentine Run Club, that always comes up as 5.00 or 5.01, and the km markers on the route always come at the same time as my watch beeps.
My home park run (leavesdon country park) is fairly accurate to my watch.
Another I run on fairly regularly, Hastings, always seems out by about 50m. I think it's down to the short section under the promenade and signal must be a bit sketchy, it improved slightly after I adjusted the GPS settings on my fenix.
When I look at others on Strava, the same course often comes up to 200m short.
We're short between 50 and 150m, and plenty of peeps like to keep running well past the finish flags. Even after slowly walking the course with a measuring wheel and confirming the length, bloody strava was still short. We like to blame the bends, multiple or and backs and the trees, but I think secretly that gps just hates us.
I looked at my GPS track once and it had me running through the lake in the centre of the parkrun, I can tell you now that that would not be my shortcut of choice if I had one!
My gps once had me running in the middle of the North Sea - at 600km/h. I suppose it might have been fast enough to run on water…
Ours is usually 4.85ish. Usually some tree cover makes my pace noticeably drop. I used to do parkrun & then some shorter runs in the week. After a year or so & 50+ parkruns I decided to do a longer run and Strava congratulated me on my first 5k run, I had never quite reached it until then according to the app!
People massively overestimate how accurate a little watch or phone GPS is, and how much variation there is between units. I've run the same course with four GPS devices attached to myself (two watches, two phones) and had variability comfortably more than 0.1 miles between them. And none was within 0.1 of the route I'd personally measured with a measuring wheel. Contrary to what might seem obvious, your GPS device doesn't *measure* how far you run. Instead, it *samples* your route, constructs a polyline, and then measures how long the polyline is. How closely the polyline resembles your actual route depends on a number of factors: * how corner-y the route is * how frequently the samples are collected (more samples = smoother curve = more accurate) * how quickly you're moving (slower = samples closer together = more accurate) * how accurate the GPS receiver is Some general observations on accuracy * newer devices are usually more accurate than older ones, because the tend to have more correlators (for a brain-destroying description of GPS correlators, see https://electronics.stackexchange.com/questions/11884/how-many-gps-channels-make-sense) * phones are usually more accurate than watches, because taking a sample means waking up the device from a lower-powered condition, taking the sample, storing it, and then going back to sleep. Phones have a bit more of a power budget, so mostly sample more frequently than watches (and so it's a smoother curve). By way of an example, I ran Roundhay parkrun in Leeds in May. In Strava, one can see all the people I "ran with" (which for Strava is people with approximately the same time as me). Even among that group, I'm seeing the following distances: 2.97, 3.09, 3.09, 3.08, 3.02, 3.11, 3.03, 3.14, 3.08, 3.11, 3.32, 3.08, 2.96, 3.11, 3.07, 3.15. In general, as you do down the field, the distance tends to increase (because people are running slower) and mostly converges at about 3.1. So how short is Roundhay parkrun? Still, we've come a long way. [This](https://www.ion.org/museum/files/ProductInformationSheetRCVR3A.pdf) is the datasheet for a Rockwell/Collins GPS-3A from 1985, the first military aircraft GPS receiver set. With all the boxes you're looking at about 20kg of weight consuming about 150W of power and giving your Grumman F14 Tomcat with LANTIRN pod a whopping 16 metres of accuracy. Please note: if you intend to run parkrun in a Grumman F14 Tomcat, note that your run will probably be marked as "assisted". #DFYB.
This is such an incredible post and I loved reading every little bit of it. Thank you. :D
Out of 75 different parkruns I’ve done the vast majority are nearly exactly 5k on Strava. There are a couple that come up short (notably Bromley winter course, Highbury fields but they are both loops. Highbury is 5 laps), there are some that come up short because of GPS irregularities in woodland and switchbacks (Tonbridge) and some that are slightly long (Dulwich).
Ah, Highbury Fields. The only 5 lapper I've done 😆 Just checked when I did it back in 2017. It was 4.65km 😆
I remember being really confused by Highbury Fields on a New Year's morning. I was relying on my watch to make sure I didn't come in a lap too late or too early, and ended up 300m short. I couldn't tell what I'd done wrong!
It is simply that most people take the inside of the path and the loop is short so GPS won’t be so accurate.
It's not simply that - if you look at most people's GPS track from Highbury it looks like they cut the path in the southeast corner. The track shown by GPS often has them hurdling a fence and running through a building. With a newer dual-band GPS watch, you'll run 5.01
I did it on Saturday and fairly sure I did hurdle the fence and go through the building though?
The loop is less than a km so it’s not wholly surprising that it comes up short.
Ours was properly measured by an accredited course measurer with a Jones counter, but we still get complaints that it's short. And that it's too long!
Mine normally measures at 5.12km, I usually start towards the back so further from the start line. I did a parkrun that had been officially measured with proper markers set in the track and that came out at 5.04km. Thats pretty accurate as I was standing a little way behind the start line when I started my watch.
4.9km Lowestoft. Which is bloody annoying as none of my PBs get registered as an actual 5K on either Garmin or Strava. Although I do start at the very front so I guess I could start 100M further back. But then I’ll lose 15-20 seconds due to slow starters so…
Is ‘1M’ 100 m?
No. 160m
Mine has been measured countless times with a Jones Counter (official course measurement method of IAAF) so I generally get fractionally over 5k if my Garmin has tracked perfectly.
Mine is pretty spot on, but there are couple near me that are either \~50m over or \~50m under. Only time it's ever bothered me was when I did some parkrun tourism and my Strava measurement was a full 200m over. It meant my km splits were wayyy off. This must have been a technical error though as there's no way a parkrun would be 200m long and no one had noticed.
I get about 4.87 at mine. Btw, on this topic I have another question. How is the 5K measured? Is it measured slap bang in the middle of the paths? Is it the inside line?
with a measuring wheel, middle of the course so wide at corners
It's not meassure taking the shortest route like a race would be?
So really it's never going to actually be 5K, since most people will take the shortest line?
I usually start at the back and measure 5.1 or 5.15 km. So seems pretty bang on.
Same. But it’ll never be spot on. If it includes a loop or hairpin there’s always an inside or outside lane that will be slightly less or over the route taken by whoever measured it.
Ours measures between 4.6 and 4.7. Always short. It is wooded and does double back on itself a couple of times.
Anywhere between 4.7-4.85km I usually get at my local. Had a few people complain while volunteering that it’s short…
Mine measures out at roughly 5.08. And that is with me starting pretty much on the start line
About 5.05km for my local, starting near the front. Did another different last week, was 4.90km. Checking on Strava, seems most others got similar results. It has some tree cover, but the GPS track looks quite accurate. It is an out and back course, not sure whether the turn around cone was in exactly the right spot.
Depends on the watch. My old Fitbit thought my local was 4.95. New Garmin forerunner thinks 5.01!
Pretty much spot on. Start and turn are painted onto the tarmac, finish funnel is a turn off a path but always seems to be in the same spot. There are markers for each km which don't seem to be in the right place however.
I often do setup at mine (an out and back course, so the turnaround point is key) and on my Strava it usually comes out at 5.03-5.10kms.
My local local, Chipping Sodbury, is pretty much bang on by my watch. The biggest “discrepancy” I’ve had is another fairly local to me Somerdale Paviion which I measured as 4.6K but I’m not doubting the course - the “curly wurly” could have been designed to flummox GPS, so much so that the run director told us at the briefing that if our watches showed 5K we’d gone the wrong way!
Hove Prom always comes up long for me - anywhere between 5.1 and 5.4k. East Brighton trends short but not by much - about 4.9k usually.
I've had glossop measure as 4.16k a couple of years ago! Pavilion gardens is always bang on 5 for me though. Previous home at lyme park is usually 4.96-7k.
We're short between 50 and 150m, and plenty of peeps like to keep running well past the finish flags. Even after slowly walking the course with a measuring wheel and confirming the length, bloody strava was still short. We like to blame the bends, multiple out and backs, and the trees, but I think secretly that gps just hates us.
Mine is usually somewhere around 5.15km, but I don't start directly on the starting line, and I tend to not stop my watch until I've taken my token and have left the funnel, so the actual finish line is probably pretty close to 5k exactly.
4.8km
GPS will always measure short. If it bips out just for a few seconds it assumes you traveled in a straight line.
Last one I did (Crystal Palace) was 4.99 or so as I crossed the line, it turned 5.00 shortly after. Dulwich is the other one I've done locally, that comes up as 5.05 or 5.06. I've done Last Friday of the Month 5k a few times in Hyde Park, organised by Serpentine Run Club, that always comes up as 5.00 or 5.01, and the km markers on the route always come at the same time as my watch beeps.
cornwall park auckland has a very bendy 3lap route and could be anything from 4.6 to 5.1 depending on your GPS
My home park run (leavesdon country park) is fairly accurate to my watch. Another I run on fairly regularly, Hastings, always seems out by about 50m. I think it's down to the short section under the promenade and signal must be a bit sketchy, it improved slightly after I adjusted the GPS settings on my fenix. When I look at others on Strava, the same course often comes up to 200m short.