According to international standard UNI EN 1334:1998, the measurement of a mattress’s width, length, and thickness must be carried out using a rigid measuring instrument. The mattress should be placed on a perfectly flat surface, and a rigid bar must be applied to the ends of each side being measured to accurately determine the overall dimensions of the product.

For example, when measuring thickness, the correct value is not the distance between the upper and lower piping edges (which would be a partial and inaccurate measurement), but rather the distance between the highest point of the upper surface including the volume of quilted padding and the corresponding point on the opposite side (see illustration below).

The same methodology must be applied when determining the width and length of the mattress. The UNI standard also allows for a tolerance of ±2 cm in both width and length compared to the nominal dimensions stated on the label. This is because, for a padded product made from a complex combination of soft and elastic materials, it is impossible to achieve or verify exact millimeter precision during either production or measurement.