# Math Help - change of variable in a surface integral

1. ## change of variable in a surface integral

Hello. I was asking if there exists a change of variable formula for suraface integrals.
I know that if $\lambda$ is the Lebesgue measure in $R^n$ and $\phi$ is a diffeomorphism of open sets of $R^n$, I can write
$x=\phi(y)\Rightarrow\lambda(dx)=|detJac(\phi)(y)|\ \lambda(dy)$ .
But if I consider $\sigma$, the p-dimensional Hausdorff measure (p<n), and $\psi$ is a diffeomorphism of two p-manifolds of $R^n$, does it exist a similar formula? like
$x=\psi(y)\Rightarrow\sigma(dx)=??\ \sigma(dy)$

nobody?