"Hawking estimated that any black hole formed in the early universe with a mass of less than approximately 10^15 g would have evaporated completely by the present day."
And the relevant part from the article discussing it:
> The original idea dates back to the 1970s with the work of Stephen Hawking and Bernard Carr. Hawking and Carr reasoned that in the universe’s first fractions of a second, small fluctuations in its density could have endowed lucky — or unlucky — regions with too much mass. Each of these regions would collapse into a black hole. The size of the black hole would be dictated by the region’s horizon — the parcel of space around any point reachable at the speed of light. Any matter within the horizon would feel the black hole’s gravity and fall in. Hawking’s rough calculations showed that if the black holes were bigger than small asteroids, they could plausibly still be lurking in the universe today.
This theory proposes the black holes would be big enough to still be around.
https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e...
"Hawking estimated that any black hole formed in the early universe with a mass of less than approximately 10^15 g would have evaporated completely by the present day."