# How is "specific gravity" defined?

$\text{Specific gravity"=rho_"substance"/rho_"reference substance}$
And the $\text{reference substance}$ is typically water, for which under standard conditions, ${\rho}_{\text{water}} = 1 \cdot g \cdot m {L}^{-} 1$, or $1 \cdot g \cdot c {m}^{-} 3$.
And thus the product ${\rho}_{\text{water"xx"specific gravity"=rho_"substance}}$ $=$ $0.67 \cdot g \cdot c {m}^{-} 3$.