Our use of magnetic field data is all in an arbitrary unit (a.u.) value for use in the sensor. We normalize the data to 1 during factory calibration and the Magnetic Field Mapper (MFM) procedure since it allows us to use magnetic field readings most effectively as an absolute reference to earth's magnetic field.
In our factory environment, the conversion to get magnetic field strength is approximately 0.49 Gauss for each 1 a.u. However this may change based on location. In general the a.u. unit is not optimized to provide an accurate estimate of the strength of the magnetic field present.
On our 10- and 100-series sensors, you are able to get the magnetic field strength measurement by reading the Sensor Component Readout (SCR) data and then using the offset, gain and misalignment information provided for the magnetometer to convert the raw 16-bit ADC value to physical magnetic field strength values. With this method you will get measurements in Gauss. The calculations will be almost exactly the same as was covered for accel/gyro measurements in this article: Converting raw 16-bit ADC values to physical values. Also please note not all calibrations will be applied in this simple model.