The recommendations for the Ca supply for maintenance of dogs have been reduced by about 75 % in the last decades. An important factor for Ca requirements is faecal Ca losses. In previous studies with experimental diets faecal Ca losses depended on Ca intake and on faecal DM excretion. A predictive equation for faecal Ca losses in mg/kg body weight (BW) developed in a fibre model is: faecal losses = −33·8 + (13·6 faecal DM excretion (g/kg BW)) + (0·78 Ca intake (mg/kg BW)). The present study aimed at testing this equation in pet food with material from trials carried out for other purposes. Digestion trials with twenty-five dry and fifteen moist foods (326 observations in total) were evaluated retrospectively. Faecal DM excretion and faecal Ca losses were significantly correlated (r2 0·86; P < 0·001). There was a highly significant correlation (r2 0·87; P < 0·001) between the experimentally determined faecal Ca excretion and the faecal Ca excretion predicted by the equation of Kienzle et al. The data from the previous fibre model study could be transferred to prepared moist and dry dog food. Faecal DM excretion has a considerable impact on faecal Ca losses in a practical feeding situation. In conclusion, Ca requirements for maintenance may vary with food DM intake and digestibility.