Accuracy of Runner GPS Watch

Zeke27 Registered Users Posts: 2
Apprentice Traveler
edited January 24 in TomTom Sports
My TT Runner GPS Watch showed just over 27 miles for my recent marathon. Just wondering if this within a normal range ( +-) or if it should be reset. Thanks!


  • tfarabaugh
    tfarabaugh Posts: 16,936
    The nature of GPS is that each data point collected is only accurate to within 15-30m of your actual location. The watch collects the data points and then tries to figure out a route using them (considering that some points may overlap or duplicate). The software then smooths the data to come up with the most reasonable route taken according to the algorithm it is programmed with. Every watch, even two of the same model, will come up with different distances, as they are collecting different GPS data. Even on a certified course the distance is a best-case scenario running 18 inches from the curb, not going around anything and taking all tangents. In addition, measured courses add 1 meter per kilometer as a buffer so they are always a bit long. Even championship marathoners run loner than 26.2 miles in a race. It is totally normal.

    I hope this helps answer your question. If so, please mark it as a solution so others can look for it if they have the same question.
  • Zeke27
    Zeke27 Registered Users Posts: 2
    Apprentice Traveler
    Thanks for the info and quick response!