I have MPU9250 IMU, which I am working on to get orientations from the sensor output data. While exploring the MPU9250 (also other sensor such as BNO055) datasheet I came across the full scale range for accel & gyro given as ±2 ±4 ±8 ±16 (g) and ±250 ±500 ±1000 ±2000 (deg/s). I did not understand what it signifies, but seems important.

I tried searching online related to full scale range but did not get explanation regarding it. I request if someone could help me in understanding by providing good explanation or a source which I can go through, I'd really appreciate that.

Also which one would be better to use?

Thanks.

_{I originally wrote this answer for this Drones.SE thread and am reposting here.}

TL;DR:

The configurable scale ranges for the accelerometer, gyroscope, and magnetometer on the MPU-9250 IMU affect the maximum resolution and range of the reported values.

As you increase the full-scale range setting, the maximum value/rate that can be reported by the IMU before the IMU is saturated increases, but the resolution of the value/rate decreases.

Section 3.1 of the datasheet for the Invensense MPU-9250 has a table that states the "Gyroscope ADC Word Length", which represents how large the values reported over the I²C or SPI interfaces are. In this case, the gyro word length is 16 bits. A 16 bit two's complement binary number (explained wonderfully in this video by Ben Eater) can range from -32768 to +32767.

Take the example of the ±500 °/s full-scale range. The unit resolution of the two's complement value reported by the gyro (aka Least Significant Bit/LSB resolution) in the ±500 °/s full-scale range is: 32767 / 500 = 65.534 LSB/(°/s) (degrees per second per LSB). This is not coincidentally labeled in the graph as the "Sensitivity Scale Factor" for the FS_SEL=1 condition.