Teaspoons to mL Converter

Article — Teaspoons to mL Converter

Teaspoons to Milliliters Conversion Guide

One metric teaspoon equals exactly 5 milliliters. One US customary teaspoon equals 4.92892 mL, defined as 1/6 of a US fluid ounce. The two values agree to within 1.4%, close enough that most cooks treat them as interchangeable. For medication, the FDA recommends mL-only dosing — a teaspoon pulled from a kitchen drawer can hold anywhere from 2 to 9 mL, a 4x error range that has caused real overdoses in children.

About 20,600 monthly searches in English ask the teaspoon-to-mL conversion, mostly people reading a recipe or a medication label. This guide walks through every teaspoon standard, the math behind each, and the safety story that pushed the US drug industry from teaspoons to milliliters.

Teaspoons to mL, the short version

To convert teaspoons to mL, multiply by the teaspoon volume:

• Metric tsp × 5 = mL. 2 tsp = 10 mL. 3 tsp = 15 mL
• US customary tsp × 4.929 = mL. 2 tsp = 9.86 mL. 3 tsp = 14.79 mL
• Imperial UK tsp × 5.919 = mL. 2 tsp = 11.84 mL. 3 tsp = 17.76 mL
• Australian tsp × 5 = mL (same as metric)

To convert mL back to tsp, divide by the same factor. 5 mL is 1 metric tsp or 1.01 US tsp. 10 mL is 2 metric tsp or 2.03 US tsp. The 1.4% gap between US and metric teaspoons is invisible in any kitchen and irrelevant for medication doses up to about 30 mL.

Four teaspoon standards, one converter

Four teaspoon volumes are in current use, with a 20% spread between smallest and largest:

US customary (4.92892 mL) — the default in the converter above. Used in American home recipes and pre-2011 US drug labels. Defined as 1/6 of a US fluid ounce, going back to the 19th century.

Metric (5 mL exact) — adopted internationally for cooking and modern pharmacy. Used in the EU, Canada, New Zealand, and modern Australian recipes. The basis for almost every modern medication dosing instruction.

Imperial UK (5.919 mL) — defined as 1/3 of an imperial tablespoon, an older British standard. Appears in pre-1970s British recipes. Modern UK recipes have switched to metric teaspoons or grams.

Australian (5 mL) — the same as metric for teaspoons. The Australian wildcard is the tablespoon, which is 20 mL (4 tsp) instead of the 15 mL (3 tsp) used everywhere else.

Teaspoons vs tablespoons

In every common system except Australia, 1 tablespoon equals 3 teaspoons. That means 1 metric tbsp = 15 mL. 1 US tbsp = 14.79 mL. 1 imperial UK tbsp = 17.76 mL. The 3-to-1 ratio is consistent enough to memorise.

The Australian tablespoon is the outlier at 20 mL (4 teaspoons). It came from a 1970s metrication decision that harmonised the Australian tbsp with the historical dessertspoon, rather than with the international 15 mL tablespoon. The result is a 33% gap that catches international cooks.

Teaspoons in medication dosing

The FDA and the American Academy of Pediatrics have spent the past 15 years pushing US drug labels toward mL-only dosing instructions. The reason is a measured safety problem: parents using kitchen teaspoons to dose children's liquid medication have over 30 times the error rate of parents using calibrated oral syringes with mL markings.

The mechanism is simple. A teaspoon pulled out of a kitchen drawer is not 5 mL. Real measured volumes range from 2 mL to 9 mL across common cutlery. A parent thinking they delivered “one teaspoon” might have given less than half the intended dose, or close to double. For acetaminophen, ibuprofen, or anything narrow-window, that variance matters.

The PROTECT Initiative — a partnership of the CDC, FDA, AAP, and others — pushed the labelling change. In 2016 the FDA recommended that all liquid OTC medication labels list doses in mL only, with the manufacturer supplying a calibrated oral syringe or dosing cup. Spoon-dosing errors fell from 31% of parents to 15% after the labelling change.

Common teaspoon-to-mL conversions

The most-searched teaspoon values are 1, 2, 1/2, 1.5, and 3. They are the building blocks of most recipes and pediatric doses:

• 1/8 tsp ≈ 0.6 mL (a pinch)
• 1/4 tsp ≈ 1.25 mL (smallest common measure)
• 1/2 tsp ≈ 2.5 mL (typical infant dose)
• 1 tsp = 5 mL metric, 4.93 mL US
• 1.5 tsp = 7.5 mL metric, 7.39 mL US
• 2 tsp = 10 mL metric, 9.86 mL US (typical pediatric dose)
• 3 tsp = 15 mL metric (1 tbsp), 14.79 mL US
• 4 tsp = 20 mL metric (1 Australian tbsp)
• 6 tsp = 30 mL metric (2 tbsp, 1 US fl oz)
• 12 tsp = 60 mL metric (1/4 cup)
• 48 tsp = 240 mL metric (1 FDA legal cup)

The kitchen-spoon variability problem

A 2011 PMC study measured the actual volume of teaspoons pulled randomly from kitchen drawers. The smallest held 2 mL. The largest held 9 mL. The median was about 5.5 mL — close to the 5 mL standard, but the spread was wide enough to matter for medication.

For cooking, a 1–2 mL error in “a teaspoon of vanilla” will not be tasteable. For a baking recipe that calls for 1 tsp of baking powder, the difference between 3 mL and 7 mL of leavening can flatten a cake. For a 2-tsp pediatric ibuprofen dose, the difference between 4 mL and 18 mL can move from underdose to potential toxicity. Measuring teaspoons are calibrated. Eating teaspoons are not.

The Australian tablespoon trap

The Australian tablespoon is 20 mL — 33% larger than the rest of the world's 15 mL tablespoon. The decision dates to the 1970s metrication of Australian cooking measurements. Many traditional Australian recipes had been written assuming a four-teaspoon dessertspoon. When Australia switched to metric, the government chose to round the tablespoon up to 20 mL rather than down to 15 mL, to preserve compatibility with existing recipes.

The result is a documented compatibility problem. A Sydney cook reading a London recipe that calls for “2 tbsp butter” will use 40 mL of butter instead of the intended 30 mL — 33% more. Going the other way, a London cook reading a Sydney recipe will under-fat the dish by 10 mL per tbsp. Australian recipes commonly print a header line noting that they use 20 mL tablespoons.

A short history of the teaspoon

The teaspoon entered English cookery around 1660, when tea was a new luxury good in Britain. Early teaspoons were small — tea was taxed at over 100% and brewed strong, served in small cups. As tea taxes dropped after the 1784 Commutation Act, cups grew and teaspoons grew with them. By the 1730s, the teaspoon had stabilised as roughly one-third of a tablespoon.

The 20th century brought standardisation. The US customary teaspoon was fixed at 1/6 of a US fluid ounce (4.92892 mL). The metric system rounded it to 5 mL exactly. Modern pharmacy and cooking both default to the 5 mL number — the 1.4% gap from the US customary value is too small to matter in any practical context.