No, I have not certified a course before, but I have mad respects for all that do. Just like I have lots of respect for anyone that volunteered their services at any capacity whether it's handing out water to being a race director to being president to a local running club.

.1 mile off is actually in some cases planned purposely (or very close to that) by race coordinators. It's to guarantee that a race is not run too short. Most certified courses are planned to be slightly longer for that reason.

The other thing I try to remember that even if the course is certified, the mile markers generally are not. So yes the entire course should be pretty close but the mile markers are measured out and set up likely with far less precise technology. I consider the mile markers to be just general information.

As a point of reference, large races use professional GPS race mapping tools. However, these tools calculate "shortest possible distance". This means that if you somehow take every turn, bend and straight-away on the same exact plot the GPS tool had calculated, your GPS device will measure the exact same distance. I had tried this out with a few Rock 'n Roll races. Keep in mind though, if you are the type of person that likes avoiding others and dodging and getting around clusters, you may find your distance on your device is longer than the race. Likewise, you may find your final distance on your GPS device is less than the actual race, which happened to me at Pittsburgh Half Marathon a few years ago (I was super impatient and took lots of sidewalks to bypass clusters). And of course I hurt my ankle doing this...lesson learned.

You will find many personal tools like Garmin and Map My Fitness are pretty close to accurate to the professional tools. In addition, you will find that if you dual GPS device on a run that you mapped out on one device, the other device will usually be almost spot on with the mapped device. Sorry for the lengthy response.

Short story long, the certified race distances are almost always correct.

Thanksgiving 5k this year was my 3rd race that regisgtered short on my Garmin. Had a 5k 0.04 short, a HM 0.3 short, and this last one 0.05 short. However, 2 other runners who also track on Strava, showed the 5k this year as right on 5k. I may have run a tiny bit less because we were supposed to stay left side of the road, and I did cut some tangents tighter than that.

I ran a marathon a few years ago with a pacer who is also a certifying official. As someone earlier said, because of the way they have to measure tangents and stay close to the curb it is virtually impossible for you as the runner to follow the path they measured. A properly marked and measured marathon should show ~26.4 on your Garmin. If you get 26.2 the course was short.

Just a note, friend recently completed a marathon with his Polar watch showing 25.9. I shot him an email so I could relay his story...turns out he was cutting onto sidewalks A TON to get around groups because he got to his race late and was in the last corral. The race was through a city with tons of turns. So there are some cases where a large difference is legit. But typically if your GPS is comes in more than .2 miles under, as @DavidMartinez2 said, the course was short.

DavidMartinez2 wrote: »

I ran a marathon a few years ago with a pacer who is also a certifying official. As someone earlier said, because of the way they have to measure tangents and stay close to the curb it is virtually impossible for you as the runner to follow the path they measured. A properly marked and measured marathon should show ~26.4 on your Garmin. If you get 26.2 the course was short.

There is also the issue of GPS error. If you run a straight line, the GPS may spot you at points to the right and left of where you are. Connecting the dots produces a longer distance than you ran. Less commonly, GPS spotting may have you cutting corners that you didn't really cut to produce less distance.

I've been thinking about this since Garmin showed 3.12 miles for my Reindeer Run 5K last Saturday. I typically see about 3.14 miles for a certified 5K when I'm running reasonably good tangents; but Saturday there was snow everywhere. Running good tangents was out of the question. I ran for the least bad footing. So what happened? *shrug* GPS isn't 100% accurate.

My marathon was on a course with minimal turns (maybe a half dozen) and only 360 runners so bunching up was not a problem after the first few turns. I still logged 26.33 miles on my Garmin.