About

Confusion between volume measurements is a frequent source of error in both culinary arts and laboratory sciences. The term "ounce" is ambiguous; it can refer to weight or volume, and even within volume, the US Fluid Ounce differs significantly from the Imperial (UK) Fluid Ounce. This tool eliminates that ambiguity by forcing a distinction between the two standards.

A US Fluid Ounce is defined as 1/128 of a US Gallon, while an Imperial Ounce is 1/160 of an Imperial Gallon. Mistaking one for the other introduces a discrepancy of approximately 4%, which is critical in chemistry, medication dosing, or large-scale beverage production. This converter provides exact metric equivalents for both systems.

Formulas

The conversion logic depends entirely on the chosen system standard.

For US Customary Fluid Ounces:

V_(ml) = V_{(US oz)} × 29.5735296

For Imperial (UK) Fluid Ounces:

V_(ml) = V_{(Imp oz)} × 28.4130625

Note: The US Fluid Ounce is derived from the US Gallon (231 cubic inches), whereas the Imperial Fluid Ounce is based on the volume of 10 pounds of water at 62°F.

Reference Data

Fluid Ounces (fl oz)	US Customary (ml)	Imperial UK (ml)	Common Vessel
1	29.57	28.41	Shot glass (varies)
2	59.15	56.83	Double shot / Espresso
3.4	100.55	96.60	TSA Carry-on Limit
4	118.29	113.65	Small wine glass
6	177.44	170.48	Teacup
8 (1 Cup)	236.59	227.30	Standard Mug
12	354.88	340.96	Standard Soda Can
16 (1 Pint)	473.18	454.61	US Pint Glass
20	591.47	568.26	Imperial Pint
25.4	751.17	721.69	Wine Bottle (750ml)
33.8	1000.00	960.36	1 Liter
40	1182.94	1136.52	Liquor Bottle (large)
67.6	2000.00	1920.73	2 Liter Soda
128 (1 Gal)	3785.41	3636.87	US Gallon Jug

Frequently Asked Questions

If the recipe source is American (e.g., US websites, cookbooks), use "US Customary". If the recipe is from the UK, Canada, or Australia, select "Imperial (UK)". If unsure, measuring by milliliters or grams is safer than volume.

Technically, yes. Volume changes with temperature (thermal expansion). However, fluid ounces and milliliters are defined units of space, not mass. So, 8 fl oz of hot water fills the same space as 8 fl oz of cold water, though the hot water will weigh slightly less.

Historically, they were based on different wine and ale gallons. The US adopted the Queen Anne Wine Gallon (1707), while the UK overhauled their system in 1824 to the Imperial Gallon. This divergence resulted in the US fluid ounce being roughly 4% larger than the Imperial fluid ounce.

Only for water (approximately). "A pint's a pound the world around" is a rough US adage meaning 16 fl oz of water weighs about 16 oz (1 lb). However, for denser liquids like honey or lighter ones like oil, volume (fl oz) does not equal weight (oz).