Teaspoons to milliliters (tsp to ml) conversion factors are listed below. To find out how many milliliters in teaspoons, multiply by the right factor or use the converter below if converting from US tsp. 1 Teaspoon [US] = 4.92892159 Milliliters. 1 Teaspoon [Metric, Australia] = 5 Milliliters. 1 Teaspoon [UK] = 5.91938802 Milliliters. Teaspoon is a volume unit mostly used in cooking recipes and prescriptions. 1 US tsp is about 5 milliliters and 1/6 of fluid ounces. The abbreviations are tsp, ts. Milliliter is a volume unit in metric system. The abbreviation is ml.