Every year, we field a few questions from marathon participants who wonder why the distance showing on their GPS watch is different than the 42.2K marathon course distance. Typically, they report that their GPS says they ran longer than 42.2K.

That's a good question and we're glad you asked it. In brief, the answer is in three parts:

  1. Certified 42.2K marathon courses, such as the QCM 42.2K course, are measured and certified using a standard procedure that is used and recognized by marathon courses around the world. It's extremely accurate, is measured using tangents (i.e. the straightest possible path), and is calculated via multiple measurements in accordance to Athletics Canada regulations. The current Athletics Canada certification number for the Queen City Marathon 42.2K marathon course is SK-2016-018-BDC. Please note that our 21.1K, 10K, 5K, and Mini Marathon courses are not officially certified.
  2. Hardly anyone can run a marathon as straight as the course is measured. There is always some weaving around other runners, swerving over to a water station, running wide on a curve, etc.
  3. Consumer GPS watches, while extremely handy for training purposes, cannot measure distances accurately enough to be used for certified course measurement. That's why certifed courses are never measured with GPS watches.

Below are two very informative and detailed articles regarding how race courses are measured and certified, and how your running pattern and the limitations of your GPS watch will affect the final reading you see at the end of 42.2K.

Click on the links below to read and download the articles. We hope this information will help in answering your questions.

In GPS we trust.

Is your GPS watch accurate on race day?