Milliliters.
to measure a small trashcan
inches
Millimetre.
if large,pints if small,ounces if medium,cups
inches because there small enough
You would use millimeters (mm) to measure the thickness of a house key, as it is a small unit appropriate for measuring such dimensions.
You would typically measure the mass of a snowflake in the metric unit of milligrams (mg), as snowflakes are very small and light objects.
Milliliters, sometimes liters
Inches or Centimeters would be small enough to measure a teacup.
The unit that the rain gauge and measuring flask measured is centimeter
You would typically use millimeters (mm) to measure the thickness of a coin. This unit is commonly used for measuring small distances or thicknesses.
You can use cups to measure a small can of juice.