A touch input determining method applied to an electronic apparatus with a touch sensing device, which comprises: (a) determining a size for a region of the touch sensing device that an object provides at least one touch input to; (b) if the size is larger than or equals to a first predetermined value, not determining the touch input is a valid touch input; and (c) if the size is smaller than or equals to a second predetermined value, not determining the touch input is a valid touch input, wherein the second predetermined value is smaller than the first predetermined value.