1) a number that equals the total quantity of <#perf=perforation> holes (or <#teeth=teeth>) within the space of 20 mm. For example, the Wildlife Conservation Issue of 1970 (<#scott=Scott> 1392) is said to have a perforation gauge of 11 x10 ½. When referencing perforations, the horizontal perforation gauge is given first, and then the vertical. 2) a tool that measures the total quantity of perforation holes (or <#teeth=teeth>) within the space of 20 mm.