SI Unit of gravitational constant is Nm²kg^-2 (Newton Meter Squared per Kilogram Squared).

The SI unit for the gravitational constant, often represented as “G“, is the newton-meter squared per kilogram squared (N·m²/kg²). This fundamental constant appears in Isaac Newton’s law of universal gravitation and Albert Einstein’s theory of general relativity, governing the gravitational force between objects. Its precise value is 6.674 × 10^(-11) N·m²/kg².

As per the universal law of gravitation:

F=G×(Mm)/d²
G=Fd²/Mm

where:
F is the Gravitational force, whose SI unit is Newton (N)
d is the Distance between the objects, whose SI unit is metre (m)
M, m are the respective Mass of the objects whose SI unit is kilogram (kg).

Hence, the SI unit of Gravitational Constant is Nm²kg^-2