Answer by taking a quote from the following article:

Ukrainians (Ukrainian: ukrayintsi, ukrayintsi, [ukra'jinjtsji]) are an East Slavic ethnic group native to Ukraine, which is by total population the sixth-largest nation in Europe. The Constitution of Ukraine applies the term 'Ukrainians' to all its citizens. Also among historical names of the people of Ukraine, Rusyns (Ruthenians), Cossacks, etc. can be found. According to most dictionary definitions, a descriptive name for the "inhabitants of Ukraine" is Ukrainian or Ukrainian people.

Most ethnic Ukrainians live in Ukraine, where they make up over three-quarters of the population. The largest population of ethnic Ukrainians outside of Ukraine lives in Russia where about 1.9 million Russian citizens consider themselves ethnic Ukrainians, while millions of others (primarily in southern Russia and Siberia) have some Ukrainian ancestry. The inhabitants of the Kuban, for example, have vacillated among three identities: Ukrainian, Russian (an identity supported by the Soviet regime), and "Cossack". Approximately 800,000 people of Ukrainian ancestry live in the Russian Far East in an area known historically as "Green Ukraine". According to some previous assumptions, an estimated number of almost 2.4 million people of Ukrainian origin live in North America (1,359,655 in Canada and 1,028,492 in the United States). Large numbers of Ukrainians live in Brazil (600,000), Kazakhstan (338,022), Moldova (325,235), Argentina (305,000), Germany (272,000), Italy (234,354), Belarus (225,734), Uzbekistan (124,602), the Czech Republic (110,245), Spain (90,530-100,000) and Romania (51,703-200,000). There are also large Ukrainian communities in such countries as Latvia, Portugal, France, Australia, Paraguay, the UK, Israel, Slovakia, Kyrgyzstan, Austria, Uruguay and the former Yugoslavia. Generally, the Ukrainian diaspora is present in more than one hundred and twenty countries of the world. The number of Ukrainians in Poland amounted to some 51,000 people in 2011 (according to Polish Census). Since 2014, the country has experienced a large increase in immigration from Ukraine. More recent data put the number of Ukrainian workers at 1.2 - 1.3 million in 2016. In the last decades of the 19th century, many Ukrainians were forced by the Tsarist autocracy to move to the Asian regions of Russia, while many of their counterpart Slavs under Austro-Hungarian rule emigrated to the New World seeking work and better economic opportunities. Today, large ethnic Ukrainian minorities reside in Russia, Canada, the United States, Brazil, Kazakhstan, Italy and Argentina. According to some sources, around 20 million people outside Ukraine identify as having Ukrainian ethnicity, however the official data of the respective countries calculated together doesn't show more than 10 million. Ukrainians have one of the largest diasporas in the world.

WHAT WAS POPULATION OF EUROPE?
20 million