Test tubes don't have a specific unit of measure. The most common way to measure the volume of a test tube is in milliliters (mL).

However, you'll sometimes see test tubes marked in other units:

* Cubic centimeters (cm³): 1 mL is equal to 1 cm³

* Ounces (oz): This is less common, but some larger test tubes might be marked in ounces.

The actual unit of measure will depend on the specific test tube and its intended use.