Not everyone needs a LPM.
And a LPM is not cheap.
If you are just gonna take the laser hobby casually, you can rely on the chart above for a VERY ROUGH idea about your laser's power.
However, do bear in mind ,the burning power of lasers rely on more than just output. Divergence and beam diameters are important too.
So don't rely on the chart to save your life.
Mmhhh ok?