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Based on the black hole mass, giving that lower mass black holes have higher mass densities than higher mass black holes.

Energy Densities

`The density is dependent only upon the mass of the black hole,

ρ≈1.85×1019 1/m2

where now $m$ is the mass of the black hole in solar masses i.e. units where 1 means the same mass as the Sun. With this equation we can see immediately that a black hole with the same mass as the Sun would have the (enormously high) density of 1.85×1019 kg/m3. Alternatively, a super supermassive black hole with the mass of 4.3 billion Suns would have a density equal to one i.e. the same density as water.`

Qmechanic
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Black holes contribute to the density of baryonic matter in the universe, if they were formed from baryons after the epoch of nucleosynthesis. For example, being formed during the core collapse of massive stars.

Black holes formed prior to this are known as primordial black holes and are conventionally ascribed as an additive term to the dark matter density.

The density ascribed to individual black holes is somewhat arbitrary but if defined as their gravitational mass divided by a volume defined by an event horizon, can be very large as you point out.

ProfRob
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