I have used GPS on mobile phones for a while now to navigate to parts of fields where I have had trials located. I have always been surprised with the accuracy of phone GPS for this purpose and now there are some apps available to show just how accurate the GPS on your phone or tablet is.

Android

GPS Test is a great app with all the functionality you need for seeing exactly how your android device is using satellites and what positional accuracy it is giving. The number of downloads (well over a million) and Google Play rating (4.6 from +20000) is indication enough about the usefulness and ease of use of this app.

The app shows the number of satellites in view and being used as well as signal to noise and positional accuracy. It also shows the position of the satellites in the sky as well as the devices position, altitude and time taken to get a fix. The app can also be used as a GPS speedometer.

I used GPS Test on a Samsung Galaxy S3 which showed a positional accuracy of 3m.

The basic version is free with a plus version adding basic navigation and waypoint logging for $2.99

Apple

Unfortunately the field for Apple is much more limited. This may be due to the GPS information that developers are able to access. It seems to be that Apple only allows core position information to be available to developers rather than the more detailed information about which satellites are being accessed.

GPS Status is a very basic single page app that provides postitional information and accuracy. I found that the accuracy status only moved in 5m increments so it was hard to compare side by side with GPS test. GPS status is free.