For devices without recognized barometric altimeters, Strava calculates your activity's elevation gain by comparing the GPS data to a known basemap of absolute elevation measurements.
Our basemap is created using data from the community: By collecting the barometric altimeter measurements from any activity uploaded to Strava in the past, we are able to build a global elevation database. Not only is this basemap more accurate than previous elevation methods, but it will result in more consistent calculations between devices, both with or without a barometric altimeter.
If there is no elevation basemap data available for all or part of your activity, we will use the former method with the public database. Read more about our elevation methods here.
If you opt to correct your elevation after recording with a barometric altimeter, we will use the basemap.