
Nominal Pipe Size Conversion to Metric Size
for 3-inch pipe, which ISO designates as 80 mm. Metric Rules-Of-Thu 1 mm = about 1/25 inch = thickness of a dime 25 mm = about 1 inch (1″ = 25.4 mm) 300 mm = about 1 foot (12″ = 304.8 mm) 1 m² = roughly 10 sq. ft. (1