The ratio of a passport size photo varies depending on the country and purpose of the photo. However, for a US passport photo, the aspect ratio is 1:1 (equal height and width) . The correct size of a US passport photo is 2 x 2 inches (51 x 51 mm) . The head must be between 1 -1 3/8 inches (25 - 35 mm) from the bottom of the chin to the top of the head. The image must be in color (24 bits per pixel) in sRGB color space, and in JPEG file format. The image dimensions must be in a square aspect ratio, with minimum acceptable dimensions of 600 x 600 pixels and maximum acceptable dimensions of 1200 x 1200 pixels.