We studied the energy levels of graphene-based Andreev billiards consisting of a superconductor region on top of a monolayer graphene sheet. For the case of Andreev retroreflection we show that the graphene-based Andreev billiard can be mapped to the normal-metal-superconducting billiards with the same geometry. We also derived a semiclassical quantization rule in graphene-based Andreev billiards. The exact and the semiclassically obtained spectrum agree very well both for the case of Andreev retroreflection and specular Andreev reflection.