There are two common types of ounces: fluid ounces and avoirdupois ounces. Here's how many milliliters are in each:

* Fluid Ounce (fl oz): 1 fluid ounce is equal to 29.5735 milliliters (mL).

* Avoirdupois Ounce (oz): This is a measure of weight, not volume. It is not directly convertible to milliliters.

Therefore, when someone asks about ounces and milliliters, you need to clarify whether they are asking about fluid ounces (volume) or avoirdupois ounces (weight).