A discussion of different estimations on Muslim populations in Europe shows that the public debate on numbers reflects the problems in academia with quantifying Muslim populations. The estimation on Muslims differs widely due to the lack of methodological and conceptual consensus on the estimation on the distribution of Muslims in Europe. The article discusses different methods in demography of religion and suggest a more precisely estimation based on reliable statistic, and in countries where no direct sources are available, a different and more realistic method of calculation of Muslims.