Multi-cracking of brittle thin layers and coating is a phenomenon difficult to model especially because of the large number of cracks that may occur. It is overcome herein by conducting calculations, not on the whole structure, but only on a simplified cell that is representative of the structure by periodic duplication. The coupled criterion is applied within this representative cell (RC) and allows to predict the crack density under an increasing applied load, the length of the RC being a variable parameter of the model. Based on the simultaneous fulfilment of an energy and a stress conditions, it allows to take into account thin layers where the crack onset is energy driven and thicker layers where the stress condition governs the transverse cracking. Results are in a good agreement with various experiments found in the literature, conducted on cross-ply laminates and coated substrates.