Multilayer graphene films demonstrate superior electrical and thermal conductivity, mechanical properties, and barrier performance compared to monolayer, thereby exhibiting greater potential for industrial applications. However, the synthesis of multilayer graphene films continues to face critical challenges, primarily including uncontrollable layer numbers, incomplete understanding of growth mechanisms, and poor reproducibility and scalability in mass production. This study introduces the “fractional layer” concept and corresponding mathematical model to precisely quantify graphene layers for the first time. Using this metric, we systematically established growth principles and process windows for layer-controlled graphene synthesis on copper substrates and elucidated the multilayer growth mechanism governed by modulating the lateral growth and vertical growth kinetics. Based on this theoretical framework, the continuous preparation of 2.3-layer graphene films was achieved via industrial scale roll-to-roll chemical vapor deposition equipment, exhibiting exceptional macroscopic uniformity and demonstrating significant potential for applications in transparent, flexible electrothermal heaters. Our work will establish a solid material foundation for the industrial application of multilayer graphene films and offer novel insights into the layer-controlled synthesis of other two-dimensional materials.