A photometric reddening-free calibration for [Fe/H] valid for giant and supergiant stars of intermediate temperature, has been obtained using the Strömgren uvbyß system. Galactic supergiants, supergiants in Magellanic Clouds and galactic metal deficient red giants with spectroscopic determinations of [Fe/H] were used as calibrators. The calibration can be used to predict [Fe/H] with an accuracy of 0.33 dex and shows the potential of supergiant stars as tracers of iron abundances in other galaxies.