Four millimeters is equal to about 5/32 of an inch. Expressed as a decimal, four millimeters is equal to approximately .157 inches. There are approximately 25.4 millimeters in every inch.
It is easy to convert linear English units to metric linear units, or to convert metric units to English units. To convert millimeters to inches, divide the length in millimeters by 25.4. For example, by dividing 50.8 millimeters by 25.4, the result is 2 inches. Conversely, multiply the number of inches by 25.4 to convert the figure to millimeters. For example, something that is 100 inches long is approximately equal to 2,540 millimeters.