US Teaspoons to Imperial Fluid Ounces (tsp to fl oz (UK))

1 US teaspoon equals 0.1734737885 imperial fluid ounces (rounded).

1 US teaspoon = 0.1734737885 imperial fluid ounces

How to convert US teaspoons to imperial fluid ounces

To convert US teaspoons to imperial fluid ounces, multiply the number of US teaspoons by 0.1734737885. The factor is rounded to 10 significant digits. To go the other way, multiply imperial fluid ounces by 5.764559642 (rounded).

imperial fluid ounces = US teaspoons × 0.1734737885

Example: 10 US teaspoons = 1.734737885 imperial fluid ounces.

Pints, quarts, gallons and fluid ounces differ between the US and the UK. Units are labeled 'US' or 'imperial' to avoid confusion.

About these units

US Teaspoon (tsp)

US customaryCurrent unit

One sixth of a US fluid ounce, exactly 4.92892159375 mL. Commonly rounded to 5 mL in recipes.

Teaspoons arrived with tea. Small spoons were common in Europe from at least the 13th century, and the earliest cited mention of a teaspoon is a London Gazette advertisement from 27 December 1686. Britain's Commutation Act of 1784 cut the tea tax from 119 percent to 12.5 percent, tea became cheap, and cups and spoons grew with it. By the 1850s the culinary teaspoon had settled as one third of a tablespoon.

The US teaspoon is one sixth of a US fluid ounce, exactly 4.92892159375 milliliters, though for nutrition labels and medicine it is rounded to 5 mL. Apothecaries once called the small spoon cochleare minus, to distinguish it from the larger cochleare majus. Household spoons are poor measuring tools: one study of 71 kitchen teaspoons found volumes from 2.5 to 7.3 milliliters, which is why dosing instructions point to standard measuring spoons or syringes.

1 US teaspoon = 0.004928921594 liters (approximately).

Sources: Wikipedia: Teaspoon; NIST SP 811, Appendix B.8: conversion factors for volume; 21 CFR 101.9: nutrition labeling household measures

Imperial Fluid Ounce (fl oz (UK))

Imperial (British)Current unit

Exactly 28.4130625 mL. About 4% smaller than the US fluid ounce.

Imperial fluid ounce comes from the 1824 reform that defined the British gallon as the volume of ten pounds of water. Because a gallon was set at 160 fluid ounces, an ounce of water weighs about one ounce of mass, around 28.35 grams. That neat link between volume and weight was the point of the imperial scheme, and it explains why people long thought of fluid ounces and weight ounces as nearly the same.

Today an imperial fluid ounce is exactly 28.4130625 milliliters, one twentieth of an imperial pint. That is about 4 percent smaller than the US fluid ounce at 29.57 mL, so a US recipe using fluid ounces does not map one-for-one onto a British one. UK trade rules restricted its use in 1995, and it lives on mostly on older labels, in bars and in recipes. Twenty of them fill an imperial pint, which makes the pint the easiest way to picture one.

1 imperial fluid ounce = 0.0284130625 liters (exactly).

Sources: Wikipedia: Fluid ounce; UK Weights and Measures Act 1985, Schedule 1

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