Stretchable inorganic electronics are usually designed and calibrated under free interface condition, while the interface conditions between the devices and skins/organs in practical applications are rather complex (free, slidable, or bonded) and may switch among them. In the ideal situation, the mechanical and electrical performances have to be consistent under different interface conditions, to ensure the accuracy and robustness of the devices. Here, the effect of interface conditions on the mechanical and electrical performances is studied for stretchable inorganic electronics with different configurations by theoretical analysis, finite element analysis and experiment. A universal size design principle is proposed for stretchable inorganic electronics to work consistently under different interface conditions, i.e., the period length of the devices/interconnects has to be the same order of magnitude as the encapsulation thickness or less. To ensure the comfort of human skin/organs, micron-scale geometrical design is necessary for epidermal electronics according to the above designed principle. This finding is of great significance for ensuring the accuracy and robustness of stretchable inorganic electronics in practical applications.