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Kilogram per Cubic Millimeter Unit | All you need to know

Kilogram per cubic millimeter (kg/mm³, kilogram/cubic millimetre, kg/mm^3, kilogram/mm³) is a metric unit of density. It defines how many kilograms of mass are contained in one cubic millimeter of volume. This unit represents an extremely high density because the cubic millimeter is a very small volume.

1 kg/mm³ = 1,000,000,000 kg/m³ (one billion kilograms per cubic meter).

Conversion to Other Density Units

1 kg/mm³ = 1,000,000 g/cm³
1 kg/mm³ = 1,000,000,000 g/L
1 kg/mm³ = 6.2428 × 10²⁶ amu/Å³

Uses of Kilogram per Cubic Millimeter

This unit is rarely used in everyday calculations because real-world substances have much lower densities.
It is mainly applied in theoretical physics, astrophysics, and material science to express extremely high-density values.
Useful when describing neutron stars, black holes, or hypothetical super-dense materials.

History and Context

The kilogram per cubic millimeter follows directly from the SI system of units. While common density values like kg/m³ or g/cm³ are widely used in engineering, chemistry, and construction, the unit kg/mm³ was introduced as part of the SI coherent derived units.

It gained attention in academic and research fields where precision at very small volumes is required. Because a cubic millimeter is extremely tiny, even a small amount of mass results in very large density values in this unit.