Square micrometers to circular mils conversion calculator shown above calculates how many circular mils are in 'X' square micrometers (where 'X' is the number of square micrometers to convert to circular mils). In order to convert a value from square micrometers to circular mils (from sq μm to cmil) simply type the number of sq μm to be converted to cmil and then click on the 'convert' button.