They cannot be and the question, as stated, cannot be answered sensibly. A micron is a measure of distance, with dimensions [L]. A gram is a measure of mass, with dimensions [M].
http://wiki.answers.com/Q/How_microns_can_be_conve...

1. Multiply the number of millimeters by 1,000 microns per millimeter. For example, if you have 30 millimeters, multiply 30 millimeters by 1,000 microns per millimeter to get 30,000
http://www.ehow.com/how_7764251_convertmillimeter...

1 Determine the value in ounces (represented by "oz" in the formula) you want to convert to grams and insert it into the blank space. Ad 2 Perform the above calculation
http://www.wikihow.com/ConvertOuncestoGrams

The question makes no sense, as you are asking how to convert distance to weight. To be able to give an answer, you'd need to know what is being measured.
http://wiki.answers.com/Q/What_is_118cm_converted_...
