The Box Sizing property in CSS defines how developers should calculate the width and height of a box. Content Box is when the default height and width get applied to the content of an element. The border and padding lie outside the box. Padding Box is when the developer adds the dimensions to include the padding and content of the element. This adds a border outside the given box. Border Box is when the box dimensions apply to the border, padding and content.

The Box Sizing property in CSS defines how developers should calculate the width and height of a box. Content Box is when the default height and width get applied to the content of an element. The border and padding lie outside the box. Padding Box is when the developer adds the dimensions to include the padding and content of the element. This adds a border outside the given box. Border Box is when the box dimensions apply to the border, padding and content.