The depths at which convection starts have been calculated for main sequence stars and giant stars of various effective temperature and hydrogen-to-metal ratios. It is found that for late-type stars ofT e≲4400 K convenction stars at τ≲0.1. In metal-deficient stars convection starts at shallower optical depths compared to normal stars of the same spectral type. The larger the metal deficiency, the shallower is the depth at which convection starts. The importance of convection in the study of metal-deficient stars and late type stars are also discussed.