A calibrating method applied to an out-cell optical touch device relative to a display panel is disclosed. The calibrating method is suitable for the out-cell optical touch device that includes at least one signal sensor and at least two position sensors. The position sensors are respectively disposed on two adjacent sides of a frame of the out-cell optical touch device. The calibrating method includes acquiring a first value according to dimensions of the display panel, detecting a distance between the frame and sides of the display panel to acquire a second value, utilizing the first value and the second value to obtain an offset, and transforming touch coordinates detected by the signal sensor into screen coordinates applied for the display panel according to the offset.