The relationship between the width and the height of the image is the aspect ratio. The aspect ratio formula is used in cinema industry to present films. Most common aspect ratio used for films are 1.85:1 and 2.39:1. The common aspect ratio for computer displays are 5:4, 4:3, 16:10 and 16:9.
Pixel generally denotes picture element. The formula to find the pixels is the product of the width and height.