How to get the zeropoint magnitude? I'm working with some data and I have some values named fluxmag0 and fluxmag0err that should correspond to the zero point values and error in flux units.

The values are around $10^{13}$ for fluxmag0 and $10^9$ for fluxmag0err

I need to have the zero point error in magnitude units. If I take $2.5\log_{10}(\mathrm{fluxmag0err})$ the values are huge so I suppose it's not the way to compute this.

How can I convert these values in terms of magnitudes? 

Thanks a lot in advance for your help
Magnitude is defined relative to a standard flux of a magnitude 0 object $F_0$.

$$M = -2.5\log(F/F_0)$$

if the error is $F_E$, then $F =F_0\pm F_E$, so the magnitude M is

$$ -2.5\log((F_0+F_E)/F_0) &lt; M &lt;-2.5\log((F_0-F_E)/F_0)$$

The errors here are tiny in comparison to the measured flux, only one part in 10000, so the range of magnitudes is similarly tiny +-0.0001