Spectral type versus effective temperature calibration for giants and supergiants in low-metallicity environments. Symbol size indicates the luminosity class, with the larger symbols for supergiants. Plotted are results from this work, the Herrero et al. (2012) and Garcia & Herrero (2013) results for IC 1613, and the Mokiem et al. (2006) and Massey et al. (2004, 2009) results for the SMC. The solid black line indicates a linear fit to the stars from this paper, not including the error bars on T_eff. The red solid line is the unweighted linear fit to the SMC stars, and the blue solid line the fit to the stars in IC 1613, WLM and NGC  3109 (low-Z). The dashed blue line is an unweighted fit to all low-Z results but excluding the single O3 giant. It illustrates the sensitivity of the found relation to this point.