Calculating Resistor Wattage for Voltage Divider?
Once I have these values, how do I calculate the required wattage of the resistors R1 and R2?


Use the power equations.

$$ P = VI $$

and by various substitutions from Ohm's Law, \$ V = IR \$ we can generate alternatives:

$$ P = VI = I^2 R = \frac {V^2}{R} $$

If you have any two values of V, I and R you can calculate the power.