We show that the average lattice disorder in YBa2Cu3O6.9 films grown by ion-beam sputtering is homogeneous and can be quantified by introducing the lattice coherence length rc that is extracted from the width of X-ray diffraction rocking curves. The superconducting properties of the films are correlated with rc: Tc decreases with increasing disorder for rc≲10 nm, while the width of the resistive transition and the normal-state resistivity increase