What is the best metric unit for measuring the amount of a coffee mug?

The best metric unit for measuring the volume of a coffee mug is liters (L). Most coffee mugs typically hold between 0.2 to 0.5 liters, making liters a convenient and clear way to express their capacity. For smaller measurements, milliliters (mL) can also be used, as one liter equals 1,000 milliliters.