CCs (cubic centimeters) and mL (milliliters) are both units of volume that are equal to each other, but derived from different base units. A volume in CCs can be converted to mL simply by multiplying by 1, because 1 CC is equal to 1 mL.
The centimeter is derived from the meter, and is exactly 1 percent of a meter. A cubic centimeter is exactly 0.0001 percent of a cubic meter. The mL is derived from the liter, which unlike a meter, is already a unit of volume. A mL is exactly 0.001 percent of a liter. When measuring a given volume of liquid with a ruler, it is most practical to determine the volume in CCs or cubic meters before converting it to liters or mLs.