Oz to ml Calculator
Convert fluid ounces to millilitres for UK and US measurements. The UK fluid ounce is 28.41 ml; the US fluid ounce is 29.57 ml. Use the tabs below to convert in any direction.
Fluid Ounce Conversion Table: US vs UK
| US fl oz | ml (US) | UK fl oz | ml (UK) |
|---|---|---|---|
| 1 | 30 ml | 1 | 28 ml |
| 2 | 59 ml | 2 | 57 ml |
| 4 | 118 ml | 4 | 114 ml |
| 8 | 237 ml | 8 | 227 ml |
| 12 | 355 ml | 12 | 341 ml |
| 16 | 473 ml | 16 | 455 ml |
| 32 | 946 ml | 32 | 909 ml |
Common Drink Sizes Reference
UK Fluid Ounce vs US Fluid Ounce: The Difference
The UK (imperial) fluid ounce and the US fluid ounce are similar in size but not identical. The UK fl oz is 28.4131 ml while the US fl oz is 29.5735 ml — a difference of about 1.16 ml per ounce, or approximately 4%.
The reason for the difference is the same as with pints and gallons: the UK and US use different gallon sizes. The imperial gallon (4.546 litres) is divided into 160 fl oz, giving 28.4131 ml each. The US gallon (3.785 litres) is divided into 128 fl oz, giving 29.5735 ml each.
For everyday purposes, rounding to 30 ml per fl oz is a close enough approximation for cooking and casual reference. For medical or scientific use, use the precise figures above.
History of the Fluid Ounce
The fluid ounce originated as a volume unit corresponding to the volume occupied by one avoirdupois ounce of water. However, because water's density varies with temperature and pressure, and because different ounce standards were used in different places, the fluid ounce developed differently in Britain and America.
In Britain, the fluid ounce was originally defined as the volume of one avoirdupois ounce of water at 62°F (approximately 28.35 ml). The Weights and Measures Act 1824 and subsequent revisions standardised it as 1/20 of a pint, giving the modern 28.4131 ml.
American fluid measures were based on older English wine measures, which used a different wine gallon of 231 cubic inches (3.785 litres). Dividing this into 128 fluid ounces gives the US fl oz of 29.5735 ml.
When to Use UK vs US Fluid Ounces
Knowing which fluid ounce applies in your context is important:
- UK recipes and UK products: Use UK fl oz (28.41 ml). Older British cookbooks may still give measurements in fl oz, referring to UK imperial fl oz.
- US recipes: Use US fl oz (29.57 ml). All American recipe books and measuring equipment use the US fl oz.
- Product labels: Most products sold in both markets now show ml alongside fl oz. In the US, the FDA requires both US fl oz and ml on nutrition labels. In the UK, ml is the primary unit.
- Medical dosing: Always use ml in the UK. NHS prescriptions are exclusively in ml. If a US medical resource cites fl oz, convert using the US figure of 29.57 ml per fl oz.
- Spirits and cocktails: International bar recipes typically use US fl oz. UK pub measures (25 ml or 35 ml) do not correspond neatly to either fl oz standard.
Fluid Ounce vs Weight Ounce: Completely Different Units
This is one of the most common sources of confusion in cooking and everyday life. A fluid ounce (fl oz) measures volume — how much space a liquid occupies. A weight ounce (oz) measures mass — how heavy something is. They are fundamentally different physical quantities.
For water specifically: 1 US fl oz of water weighs approximately 1.043 weight oz (29.57 g ÷ 28.35 g/oz). But for other liquids:
- 1 fl oz of milk weighs approximately 1.073 oz (milk is denser than water)
- 1 fl oz of olive oil weighs approximately 0.96 oz (oil is less dense than water)
- 1 fl oz of honey weighs approximately 1.5 oz (honey is much denser than water)
In UK baking, this distinction matters less because British recipes specify weight in grams for solids and ml for liquids, removing the need to convert between volume and weight ounces at all.
Fluid Ounces in Medicine: Paediatric Dosing
In the UK, all medication dosing for both adults and children uses millilitres exclusively. NHS prescriptions, pharmacy labels, and medical guidance all specify doses in ml. Paediatric liquid medicines typically come with 5 ml measuring spoons or graduated syringes marked in ml.
However, some older medical reference materials — particularly US-published resources — may cite fl oz doses. Key conversions for medical use:
- 1 US fl oz = 29.57 ml ≈ 30 ml (for a rough guide)
- 0.5 US fl oz = 14.79 ml ≈ 15 ml (one standard UK medicine spoon)
- 2 US fl oz = 59.15 ml ≈ 60 ml
Critical note: For any medication dosing, always follow the instructions on the UK product label or NHS prescription, which will be in ml. Do not convert from fl oz for medication — measure directly in ml with an appropriate measuring device.
UK Pub Measures: Regulated Spirit Portions
UK pub spirit measures are tightly regulated under the Weights and Measures Act 1985. Licensed premises must serve spirits (whisky, gin, rum, vodka) in one of two standard measures:
- 25 ml (the most common UK pub measure) = approximately 0.88 UK fl oz or 0.85 US fl oz
- 35 ml (used by some pubs, particularly in Scotland) = approximately 1.23 UK fl oz or 1.18 US fl oz
Doubles are therefore 50 ml or 70 ml respectively. Customers have the right to ask which measure a pub uses before ordering. Under the Act, pubs must display their spirit measure prominently.
Note that neither 25 ml nor 35 ml corresponds neatly to a standard fl oz measure in either UK or US terms. This is intentional — the metric measures were adopted during the UK's metrication programme. For reference: the old UK gill (one-quarter pint = 142 ml) was formerly the standard spirit measure before metrication.
Coffee Shop Sizes: Starbucks and Costa
Coffee shop drinks are frequently described in fluid ounces, particularly in Starbucks' American-origin sizing system. Here is a practical guide for UK customers:
- Starbucks Tall: 12 US fl oz = 355 ml
- Starbucks Grande: 16 US fl oz = 473 ml
- Starbucks Venti (hot): 20 US fl oz = 591 ml
- Costa Primo: approximately 340 ml
- Costa Medio: approximately 454 ml
- Costa Massimo: approximately 568 ml (exactly 1 UK pint)
Baby Formula: Measuring fl oz for Infant Feeding
Baby formula in the UK is always measured in millilitres. NHS feeding guidelines specify amounts in ml for each stage of infant development. However, some American formula brands sold internationally, and some US parenting resources, may specify amounts in fluid ounces.
Key infant feeding conversions:
- 2 US fl oz = 59.1 ml (early newborn feeds)
- 4 US fl oz = 118.3 ml (typical newborn feed)
- 6 US fl oz = 177.4 ml (growing baby feed)
- 8 US fl oz = 236.6 ml ≈ 1 US cup
UK formula tin instructions and NHS guidance always use ml. If using a UK-purchased formula tin, follow the ml measurements specified. American fl oz figures are provided here only for reference when consulting US resources.
Skincare and Beauty Products: ml vs fl oz Labels
Cosmetics and skincare products sold in the UK typically display both ml and fl oz on their packaging. Products originating from the US or international markets often lead with fl oz while products for the UK market lead with ml.
Airline liquid restrictions (100 ml maximum per container in carry-on luggage) are a common context where passengers need to understand fl oz equivalents:
- 100 ml = 3.38 US fl oz = 3.52 UK fl oz
- 200 ml = 6.76 US fl oz = 7.04 UK fl oz
- A standard 240 ml bottle of moisturiser = 8.11 US fl oz (too large for hand luggage)
UK vs US Drinks Cans: Same Size, Different Numbers
One of the most interesting coincidences in Anglo-American measurement is that the standard soft drink and beer can is the same physical size in both countries — 330 ml — despite being described differently:
- UK: 330 ml can
- US: 11.2 US fl oz can (330 ml ÷ 29.57 = 11.16 fl oz)
The US also has a 12 fl oz standard can (355 ml), which is slightly larger than the UK 330 ml standard. In the UK, 330 ml is the dominant can size for beer and soft drinks; 500 ml cans are also common for premium beers. US craft beers often come in 16 fl oz (473 ml) "tallboy" cans.
Wine Pour Sizes: Fluid Ounces and ml
Wine is measured in ml in the UK for both trade and retail purposes. A standard 750 ml bottle contains:
- 25.36 US fl oz total
- 26.40 UK fl oz total
- Approximately 5 standard 150 ml glasses (5.07)
- Approximately 4.3 large 175 ml glasses
UK pub wine glass measures regulated under licensing law:
- Small (125 ml): 4.23 US fl oz / 4.40 UK fl oz
- Standard (175 ml): 5.91 US fl oz / 6.16 UK fl oz
- Large (250 ml): 8.45 US fl oz / 8.80 UK fl oz
Related Calculators
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Frequently Asked Questions
It depends which fluid ounce you mean. One US fluid ounce equals 29.5735 ml (approximately 29.57 ml or 30 ml). One UK (imperial) fluid ounce equals 28.4131 ml (approximately 28.41 ml). The US fl oz is slightly larger. For quick mental arithmetic, 1 fl oz is approximately 30 ml.
The UK (imperial) fluid ounce is 28.4131 ml, while the US fluid ounce is 29.5735 ml. The US fl oz is approximately 4% larger. This difference arises because the UK imperial gallon (4.546 litres) divides into 160 fl oz, while the US gallon (3.785 litres) divides into 128 fl oz, resulting in different fl oz sizes despite both gallon definitions descending from English measurement traditions.
No. A fluid ounce (fl oz) measures volume (space occupied by a liquid). A weight ounce (oz) measures mass (how heavy something is). One US fl oz of water happens to weigh approximately 1.04 weight oz, but this coincidence only applies to water at a specific temperature. For other liquids: 1 fl oz of honey weighs about 1.5 oz; 1 fl oz of olive oil weighs about 0.96 oz.
There are 20 UK fluid ounces in a UK imperial pint (568.261 ml ÷ 28.4131 = 20). There are 16 US fluid ounces in a US pint (473.176 ml ÷ 29.5735 = 16). A UK pint glass is 20 fl oz; an American pint glass is 16 fl oz — so an American "pint" of beer is 20% smaller than a British one.
For medicine, always use millilitres (ml) rather than fluid ounces to avoid dosing errors. If a US medication label states a dose in fl oz, multiply by 29.57 to get ml. For example, 0.5 fl oz = 14.79 ml (approximately 15 ml — one standard UK medicine spoon). NHS prescriptions and UK pharmacy labels always use ml. Always measure using a proper graduated syringe or spoon marked in ml.
In UK licensed premises, a single measure of spirits is either 25 ml (most common) or 35 ml (some pubs, particularly in Scotland). Both are legal under the Weights and Measures Act 1985. A double is 50 ml or 70 ml. The pub must display its chosen measure size. In US terms: 25 ml ≈ 0.85 US fl oz; 35 ml ≈ 1.18 US fl oz. A standard US "shot" is typically 1.5 US fl oz (44 ml), which is larger than the UK standard single measure.