Electrodeposition and other methods are employed to obtain metallic films and coatings. Copper coatings are most extensively used in circuit board industry and often as a base to further formation of other metallic films. Electrodeposited copper films (thin layers) are widely used in electronic and automotive industry so its electrical and mechanical properties and its thickness are important. Several methods are used for thickness determination of thin films and coatings for example mechanical, magnetic and ball crater with light microscopy methods. They are destructive and not precise enough. The X-ray fluorescence, absorption and diffraction are more frequently used due to better precision. Although they are complex and expensive, they pronounce an important feature like non-destructive character. For particular cases geometrical conditions and mathematical calculation procedure must be elaborated. An application of X-ray diffraction in grazing incidence angle for thickness determination is described in this article. The method is based on absorption principles of X-ray beam. The absorption is proportional to thickness of the coating and to incidence and to the diffraction angle which. Geometrical conditions were obtained experimentally and suitable mathematical calculations were introduced. The elaborated methodical approach was applied to thickness determination of copper coatings electrodeposited on a brass substrate.