More than 8 million people have fled Ukraine since Russia invaded the neighbouring country on February 24.
The other way around, more than 2.8 million people crossed the border, according to data from the UN refugee agency UNHCR.
Poland is the main destination, but many have moved on to other European countries, including the Netherlands. More than 5.2 million refugees from Ukraine have applied for protective status in Europe, according to the UNHCR.
More and more Ukrainians are returning to their country, which is relatively safe in western parts as the Russian army concentrates on the eastern Donbas region.
Ukraine had more than 41 million inhabitants at the beginning of the war, not counting the inhabitants of the Crimean peninsula, which was annexed by Russia.