I assume you're using moment magnitude [1] since it's the most common measure. In fact every 2 integers is a 1000 times increase [2] so M8 is 1000 times more powerful than M6.
[1] https://en.wikipedia.org/wiki/Moment_magnitude
[2] https://en.wikipedia.org/wiki/Moment_magnitude#Definition
https://en.wikipedia.org/wiki/Richter_magnitude_scale:
> Because of various shortcomings of the ML scale, most seismological authorities now use other scales, such as the moment magnitude scale (Mw), to report earthquake magnitudes, but much of the news media still refers to these as “Richter” magnitudes. All magnitude scales retain the logarithmic character of the original and are scaled to have roughly comparable numeric values (typically in the middle of the scale).[citation needed]
> The energy release of an earthquake,[27] which closely correlates to its destructive power, scales with the 3⁄2 power of the shaking amplitude[why?]. Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 in the energy released.[28] The elastic energy radiated is best derived from an integration of the radiated spectrum, but an estimate can be based on mb because most energy is carried by the high frequency waves.
Sounds like what they teach casually is simplified well past the point of accuracy and possibly even particular usefulness.