Horse withers height is frequently estimated based on skeletal remains during archeozoological analyses. The routinely used methods (Vitt and Kiesewalter) do not allow withers height estimation without complete long bone and skull osteometry. The modified Wyrost and Kucharczyk formula is based on the internal dimensions of the cranial cavity. This method can be used even when the neurocranium is the only surviving portion of the skull. Earlier investigation demonstrated that it can be used as a substitute for the Kiesewalter method. The statistical analyses of the results achieved using metapodial bones are strongly correlated with the results achieved using the Wyrost and Kucharczyk method. A unique horse skull assemblage, dating back to medieval times, was unearthed from several archeological sites in Poland (Silesia, Kuyavia, Grater Poland, Western Pomerania, and Eastern Pomerania). This study aimed to estimate the withers height of this assemblage using the modified Wyrost and Kucharczyk method. Subsequently, these estimations were compared with accessible literature data from both medieval Poland and surrounding territories. The literature indicates that the horses from Western Pomerania, Silesia, and Kuyavia were larger than the animals from Eastern Pomerania. Our results show that horses from Western Pomerania were larger than those from Silesia, Kuyavia, and Eastern Pomerania. In both cases, the Western Pomeranian horses are the largest. In general, according to our results and the accessible literature, it seems true that Polish medieval horse populations can be described as medium- and small-sized, according to Vitt's classification. The modified Wyrost and Kucharczyk formula can be used as an additional or alternative method of calculating withers height in routine archeozoological studies.