How to Convert Thou (Mils) to Millimeters Thou (or mil) is commonly used in engineering and manufacturing to measure small thicknesses. One thou equals 0.0254 millimeters. The Mathematical Formula To convert thou to millimeters multiply the value by 0.0254: Millimeters = Thou × 0.0254 Thou to Millimeters Table Thou (mil) Millimeters (mm) 1 mil0.0254 mm 10 mil0.254 mm 25 mil0.635 mm 100 mil2.54 mm
