To convert 4 millimeter to inch, multiply by the conversion factor 0.039370. So, 4 millimeter x 0.039370 = 0.15748 inch. For practical purposes, this is often rounded to 0.1575 inch.

4 millimeter equals exactly 0.157480 inch. For practical purposes, this is often rounded to 0.1575 inch.

Objects measuring approximately 4 millimeter include the diameter of an M4 machine screw, the thickness of a stack of five standard credit cards (3.8mm), or the diameter of a small black peppercorn (3-5mm).

Converting millimeter to inch is useful for international collaboration in engineering and manufacturing, when working with legacy equipment or designs from countries using imperial units, and for consumer understanding in regions where inches are standard.

A simple memory aid is to remember that 1 millimeter is roughly 0.04 inch. So, 4 millimeters is approximately 4 times 0.04, which is 0.16 inch. Visually, two stacked US nickels are about 3.9mm, a good reference for 4mm.