We present an area formula for continuous mappings between metric spaces, under minimal regularity assumptions. In particular, we do not require any notion of differentiability. This is a consequence of a measure theoretic notion of Jacobian, defined as the density of a suitable “pull-back measure”. Let (X, d, μ) and (Y, ρ, ν) be two metric measure spaces, where μ is a Borel regular measure on X and ν is a Borel measure on Y . The terminology “measure” refers to a countably subadditive nonnegative set function, see 2.1.2 of [2]. We also assume that μ is finite on bounded sets and that there exists a μ Vitali relation V , 2.8.16 of [2]. The first point is the notion of “pull-back measure” with respect to a continuous mapping. To do this, we need the following important result, proved in 2.2.13 of [2]. Let X be a complete and separable metric space and let g : X −→ Y be continuous. Then for every Borel set B ⊂ X, we have that g(B) is ν-measurable. Throughout, the above assuptions will constitute our underlying assumptions. Definition 1 (Pull-back measure). Let (X, d) be complete and separable, let E ⊂ X be closed and let f : E −→ Y be continuous. For each S ⊂ E, we set ζ(S) = ν ( f(S) ) . We denote by f ∗ν the measure arising from the Caratheodory’s construction applied with ζ defined on the family of Borel sets, according to 2.10.1 of [2]. We say that f ∗ν is the pull-back measure of ν with respect to f . The measure f ∗ν is automatically extended to the whole of X, by setting f ∗ν(A) = f ∗ν(A ∩ E) for any A ⊂ X. In the sequel, E will stand for any closed subset of X. Notice that f ∗ν is a Borel regular measure on E, as it follows by the Caratheodory construction. Recall that the multiplicity function of f : E −→ Y relative to A is defined as N(f, A, y) = # ( A∩f−1(y) ) for all y ∈ Y . For any Borel set T ⊂ E, Theorem 2.10.10 of [2] gives us the formula