3.4 ounces (oz) is equal to approximately 100.55 milliliters (ml). The conversion is based on the fact that 1 US fluid ounce equals about 29.5735 milliliters. So, multiplying 3.4 by 29.5735 gives about 100.55 ml. This is a commonly referenced conversion, especially for travel-size liquids where the 3.4 oz (100 ml) limit is widely recognized.