Enter the observed irradiance and the reference flux into the Calculator. The calculator will evaluate the Apparent Magnitude. 

Apparent Magnitude Formula

M = -5*log(10) (Fx/Fx0)


  • MI is the Apparent Magnitude (())
  • Fx is the observed irradiance
  • Fx0 is the reference flux

To calculate Apparent Magnitude, divide the observed irradiance by the reference flux, take the log of the result, then multiply by -5.

How to Calculate Apparent Magnitude?

The following steps outline how to calculate the Apparent Magnitude.

  1. First, determine the observed irradiance. 
  2. Next, determine the reference flux. 
  3. Next, gather the formula from above = M = -5*log(10) (Fx/Fx0).
  4. Finally, calculate the Apparent Magnitude.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

observed irradiance = 101

reference flux = 6