It seems that nobody really knows nor is motivated to investigate. The only figures available are from the early 1990's. These official estimates used by the Catholic Church hold that there are 300.000 Catholics of the Latin Rite in Western Russia, 60.000 to 100.000 (35.000 foreigners) in Moscow and about 1.000.000 in Asian Russia.
These estimates were made based upon the numbers of people pertaining to traditionally Catholic ethnic groups, Lithuanians, Poles and a percentage of Germans. Although Catholics in Russia use a principle of associating nationality and religion, (such as Poles are Catholics, therefore all Poles in Russia are to be counted within the folds of Catholicism) many do not permit the Russian Orthodox Church to use the same principle, whereby all Russians are considered to fall within the pastoral and missionary field of the Orthodox Church, that is, within her canonical territory.
However, it would seem that these somewhat romantic numbers of Catholics have been greatly on the decrease and will continue to decrease in the future. Most of the Germans have already resettled to Germany, as also have many Lithuanians and Poles returned to their ancestral patria. A further consideration is that a majority of those who are officially Poles or Germans are elderly. When they married many a decade ago, they often wedded Russians and for various family and political reasons their children were registered as Russians, consider themselves Russians and speak only Russian.
If the numbers of Catholics in Russia were to be estimated, as else where in the world, based on the numbers of those who have had official contact with the Church, through the reception of the sacraments, then a very different picture must be painted. However, it would be unfair to estimate in this way, due to the historical atheistic persecution of religion, the destruction of Churches and the imprisonment and execution of a majority of priests. In these times the faith was sometimes handed on from grandmothers and not from priests. Accordingly, no viable statistics exist.
Seemingly, the only way of determining a real number of Catholics in Russia must be based upon the numbers of faithful who frequent Holy Mass where ever and whenever it is celebrated. Thus, in Western Russia there would only seem to be about 10,000 Catholics who frequent Church on a regular basis (Moscow 3000 - 4000, St. Petersburg 2000, Kalingradskaja region 2000 - 3000, The Volga region and Urals 600 - 800, The North Caucuses 500 - 600, Central and Northern Russia - less than 500). On the major feasts of Christmas and Easter, the numbers of those coming to Church doubles and yet still the picture remains somewhat unclear due to the general practising rate among people in Russia.
Another area of concern regarding the numbering of Catholics in Russia is a process of Latinization. Catholics of other rites and religious traditions are being educated to be and counted among the Latins, in particular, the Armenians and the Greek Catholics (Ukrainians and Russian Orthodox who have become Catholics). According to the laws of the Catholic Church not only should ancient Christian religious traditions be respected and encouraged but also the faithful appertaining to these traditions are not allowed to change their tradition, that is their rite.
In the last six years there has however, been one increasing sector within Catholic circles in Russia. Many foreigners have come to Russia, as business people, as diplomats and as students. Many of these come from traditionally Catholic countries and have been baptized into and brought up in the Catholic faith. However, many have lapsed from practicing their faith and rarely frequent the Catholic Church in Russia. In Moscow there might be as many as 40,000 to 50,000 foreign Catholics, in Russia there might be even more than 100,000, most of whom are in need of the Church's attention and frequently of a re-evangelization. There are very few who see the largely abandoned foreign Catholics as the reason for a Catholic presence in Russia.