To calculate the surface area of a box, multiply the length by the width, the length by the height, and the width by the height. Multiply each result by 2 and sum them up to get the total surface area. Related calculators Depending on the type of body, there are different. Quickly calculate the volume, surface area, diagonal, and girth of any rectangular box. Essential for shipping, storage, and packaging design. LengthEnter the longest dimension of the box.