4 US fluid ounces equals exactly 118.29 milliliters, which also makes it precisely ½ cup for any cooking or baking task.
Grabbing the wrong measuring cup is the fastest way to throw off a recipe. That half-cup mark on your liquid measure isn’t always the same as 4 fluid ounces — it depends on which side of the Atlantic the recipe came from. Here’s the clean breakdown for US fluid ounces, why you’ll sometimes see 120 mL on a label, and when those 4 milliliters of difference actually matter.
What 4 fl oz Equals in Milliliters and Liters
The exact conversion is built on one standard factor: 1 US fluid ounce equals 29.57353 milliliters. That makes the math straightforward if you have a precise kitchen scale or a milliliter-marked cup handy.
- In milliliters: 4 × 29.57353 = 118.29411825 mL, almost always rounded to 118.29 mL or 118.3 mL for recipes.
- In liters: 4 × 0.0295735 = 0.118294 L, commonly rounded to 0.118 L.
- In cups: 4 fl oz equals exactly ½ US cup.
The cup equivalent is the most useful kitchen shortcut — no calculator needed if your liquid measuring cup has half-cup markings.
When 4 fl oz Is 120 mL (And When It Isn’t)
You will see “4 fl oz = 120 mL” on many bottles and food labels. That number comes from the FDA’s rounding rule for nutrition facts: on a packaged food label, 1 fluid ounce is legally allowed to be listed as 30 mL, so 4 ounces becomes 120 mL. This rounding is standard and expected on everything from salad dressing to soda bottles.
For everyday cooking, the difference between 118.29 and 120 mL is negligible. For baking or precise mixing, especially in doubled or tripled recipes, the correct value is still 118.29 mL. The short rule: a liquid measuring cup’s ½ cup line gives you an honest 4 fl oz, while a nutrition label’s “120 mL” is a legally rounded shortcut.
The Big Mistake: Confusing US and Imperial Fluid Ounces
This is the trap that most often catches home cooks following a UK or Canadian recipe. The Imperial (UK) fluid ounce is roughly 4% smaller than the US fluid ounce.
- US fluid ounce: 29.57 mL per oz, so 4 fl oz = 118.3 mL.
- Imperial (UK) fluid ounce: 28.41 mL per oz, so 4 fl oz = only 113.65 mL.
A recipe from a British food blog calling for 4 fl oz of milk is asking for about 113 mL, not 118 mL. The difference of roughly 5 mL per ounce adds up fast across a batch of pancakes or a custard. Check the recipe’s origin before you pour.
Quick-Reference Conversion Table
For the most common kitchen volumes, this table covers both US and Imperial systems so you never guess.
| Volume | US fl oz (mL) | Imperial fl oz (mL) |
|---|---|---|
| 1 fl oz | 29.57 mL | 28.41 mL |
| 2 fl oz (¼ cup) | 59.15 mL | 56.83 mL |
| 4 fl oz (½ cup) | 118.29 mL | 113.65 mL |
| 8 fl oz (1 cup) | 236.59 mL | 227.30 mL |
| 16 fl oz (1 pint) | 473.18 mL | 454.61 mL |
| 32 fl oz (1 quart) | 946.35 mL | 909.22 mL |
| 128 fl oz (1 gallon) | 3,785.41 mL | 3,636.87 mL |
Source data for the conversion formula used in this table comes from the standard US fluid ounce to milliliter calculation.
What “4 oz” Means on a Bottle Label
If you are buying bottles for homemade hot sauce, lotion, or cleaning solutions, “4 oz” on the packaging and “4 oz” of product can be two different numbers. Suppliers often label bottles by their overflow capacity — the total volume up to the rim — while the actual fill line is lower.
- Overflow capacity: The bottle holds 4 oz (120 mL) if you fill it to the very top.
- Fill capacity: The normal fill level is typically 108–114 mL, which is about 3.6 to 3.8 oz.
A bottle sold as “4 oz” in a beauty or cosmetic catalog likely holds only 3.6 to 3.8 oz of actual liquid. For production or home bottling, check the product spec sheet for fill capacity rather than trusting the “4 oz” label out of the box.
How to Convert Any Fluid Ounce Measurement Yourself
Toss the calculator for everyday cooking — most recipes work fine with the simple numbers above — but for lab-grade accuracy or large batches, the formula is worth keeping on your phone.
- Ounces to milliliters: Multiply fl oz by 29.57353. Example: 4 × 29.57353 = 118.294 mL.
- Ounces to liters: Multiply fl oz by 0.0295735. Example: 4 × 0.0295735 = 0.1183 L.
- Liters back to ounces: Multiply liters by 33.814. Example: 1 L × 33.814 = 33.81 fl oz.
For reverse conversions, the key number to remember is that 1 liter contains roughly 33.8 US fluid ounces. That translates to about 4 and ¼ cup per liter — a useful mental shortcut at the grocery store or bar.
When Precision Actually Matters (And When It Doesn’t)
Most home cooks can treat 4 fl oz as 118 mL or 120 mL interchangeably without causing a problem. The cases where you should use the exact number:
- Baking: A 4-mL difference in liquid can tighten or loosen a dough, especially in double batches. Stick with 118 mL.
- Medical dosing: Never round 4 fl oz up to 120 mL when measuring liquid medicine. Use 118.3 mL to stay within the prescribed dose.
- Chemical mixing: A 4% error between US and Imperial ounces can throw off concentrations. Verify which ounce the recipe uses before mixing.
- All other cooking: The ½ cup line on your liquid measure is accurate enough. Use it with confidence.
Which Ounce Your Recipe Relies On: A Quick Guide
The fastest way to tell which ounce standard a recipe uses is its origin. American and Canadian cookbooks use the US fluid ounce. British, Australian, and older Commonwealth recipes use the Imperial or Australian ounce (which itself is 20% smaller than the US ounce in the case of the Australian tablespoon system).
When in doubt, look at the cup volume the recipe calls for. If a recipe says “4 fl oz (½ cup),” it is definitely using US fluid ounces, because the Imperial cup is 10 fl oz, not 8.
References & Sources
- Inch Calculator. “Fluid Ounces to Milliliters Conversion.” Provides the standard conversion factor of 29.57353 mL per US fl oz.
- Calpac Lab. “Volume Conversion Calculator.” Supports the precision requirements for lab and medical use.
