How Many Milliliters Are in an Ounce?

How many ml are in 1 US fluid ounce?

1 US fluid ounce equals 29.5735 milliliters, which most kitchens round to 30 ml for simplicity. The math: a US gallon is 3785 ml divided into 128 fluid ounces, which gives 29.57 ml per ounce. For cooking, the 0.5 ml rounding doesn't matter; you won't taste the difference in any sauce, soup, or baked good. For cocktails, where standard pours are 1 ounce or 1.5 ounces and the difference between drinks adds up over a service, the precise number can matter. Bar jiggers are typically calibrated to the exact 30 ml or 22 ml measurements that match common cocktail recipes.

How does the US fluid ounce compare to UK and metric ounces?

There are two fluid ounce standards: US fluid ounce at 29.57 ml and UK imperial fluid ounce at 28.41 ml. The UK ounce is slightly smaller despite the UK pint, quart, and gallon all being larger. This is because the UK gallon contains 160 imperial fluid ounces vs the US gallon's 128 fluid ounces, so each individual ounce ends up slightly smaller. For most recipes, the 1 ml difference doesn't matter; you can use a US fluid ounce measurement for a UK recipe without noticeable issues. But it can stack up across larger amounts. A 32 oz container labeled in US ounces is 946 ml; the same '32 oz' in UK imperial would be 909 ml. The 37 ml gap is enough to noticeably shortchange a recipe that calls for the larger container.

How do common fluid ounce amounts convert to ml?

For US fluid ounces (rounded to 30 ml each): 1 fl oz is 30 ml, 2 fl oz is 60 ml (1/4 cup), 4 fl oz is 120 ml (1/2 cup), 8 fl oz is 240 ml (1 cup, rounded), 16 fl oz is 480 ml (1 pint, rounded), and 32 fl oz is 960 ml (1 quart, rounded). For precise math, multiply ounces by 29.57. For kitchen math, multiply by 30 and accept the small rounding error. The rounding starts to matter at large volumes. For baking precision, work in ml directly or weigh ingredients on a scale to skip the volume math.

When does the milliliter-to-ounce conversion matter most?

Cocktail recipes are the biggest case. Most cocktails specify pours in milliliters or ounces depending on the source. A 30 ml pour and a 1 oz pour are close enough that bartenders use them interchangeably for home use. Medicine is another situation: liquid medications are usually dosed in milliliters, but old recipes or instructions might use teaspoons or fluid ounces. The standard conversions: 1 teaspoon equals 5 ml, 1 tablespoon equals 15 ml, 1 fluid ounce equals 30 ml. International recipes are the third major case; European recipes use milliliters while American recipes use fluid ounces, and converting between them is a 30-to-1 ratio for most kitchen use. For wine and spirit pours, 1.5 fl oz (45 ml) is the standard 'shot' size in the US.