Milliliters (mL) are a metric unit of volume. One milliliter is one-thousandth of a liter. It also is the equivalent of one cubic centimeter. To calculate the volume of an object in milliliters, you must first measure the object in centimeters and find the volume in cubic centimeters. If the object is defined by other units of measurement, you will have to convert the volume before you can find the milliliter volume.