Combined Magnitude Calculator
Add the fluxes of two unresolved light sources and express their total as one magnitude.
Calculate locally
No account, API or uploaded inputs. All calculations run in this browser.
Worked example
Two sources of magnitude 5 combine to approximately 4.247425. Two equal sources are about 0.752575 magnitude brighter together; combining them does not give magnitude 10.
Method and units
Magnitudes are logarithmic, so add fluxes rather than magnitude numbers. With b = min(m1,m2), total magnitude = b − 2.5 log10[1 + 10^(−0.4|m1−m2|)]. Normalizing to the brighter source improves numerical stability.
What this result means
Both magnitudes must use the same passband and zero-point system. This sums independent source fluxes, not coherent wave amplitudes. Eclipses, variability, background subtraction, detector saturation and uncertainties are not modelled. A very faint companion may have no visible effect at displayed precision.