Symbols · Greek letters

ρ Ρ Rho

Say it: “rho” · ROH

What it means

The seventeenth Greek letter. ρ is density, the correlation coefficient, electrical resistivity and charge density.

Statistics

ρ = Cov(X, Y) / (σ_X σ_Y)

Aethel says

rho equals the covariance of X and Y, over the quantity sigma sub X sigma sub Y

the correlation coefficient

Physics

ρ = m / V

Aethel says

rho equals m over V

density is mass over volume

Pearson correlation coefficient

ρ = Cov(X, Y) / (σ_X σ_Y)

Gauss's law

∇ · E = ρ / ε₀

Navier–Stokes equation

ρ(∂u/∂t + u · ∇u) = −∇p + μ∇²u + f

How do you pronounce rho (ρ)?

It is said “rho”, roughly ROH.

What does ρ mean in maths?

The seventeenth Greek letter. ρ is density, the correlation coefficient, electrical resistivity and charge density.

How do you type ρ?

In LaTeX, write \rho, \varrho (capital: P). Its Unicode code point is U+03C1, U+03A1.

What is ρ often confused with?

It is easy to mistake for p: the capital Ρ looks exactly like a Latin P.