8 millimeters = 0.31496063 inches. This is because one inch in 2.54cm, or 1cm is 0.3937 inches. Since one millimeter is 0.1 cm you multiply by a factor of 0.8 to find 8 millimeters. If you have access to a computer when you want to do conversions, use something like google, if you type "convert [amount][unit] to [amount][unit]" it will display the conversion to about 8-10 decimal places. However, alternatively you can use conversion tables. These can be found online (normally with a conversion calculator with them). The conversion tables are handy because they display commonly used conversions: 1/4 of an inch to mm for example. A good of these online is: Mdmetric.com. However, these can lack accuracy, they are normally only to a few decimal places.
