Convert 3.4 oz to ml: TSA Rules, Cooking Tips & Common Mistakes

Converting between US customary and metric units is important in daily life. For example, 3.4 ounces to milliliters is a frequent question. Because 1 US fluid ounce equals 29.5735 mL, 3.4 fl oz × 29.5735 ≈ 100.55 mL (US). Knowing this exactly helps in cooking (for precise recipe measurements), travel (TSA limits liquids to 100 mL, which is 3.4 oz), and science (laboratory volumes). It also highlights the US vs. metric divide: unlike the US, most countries use milliliters for liquids. (As a reference, a US fluid ounce is about 4% larger than a British Imperial fluid ounce.) This guide will explain how to convert 3.4 oz to mL step by step, show handy tables, discuss the TSA 3-1-1 rule, cover kitchen conversions, and point out common pitfalls.

Quick Answer & Reference Table

Quick Answer: 3.4 US fluid ounces ≈ 100.55 mL. (For British/Imperial measure, 3.4 fl oz ≈ 96.60 mL.) These use 1 fl oz = 29.5735 mL or 28.4131 mL (Imperial). In other words, three ounces is about 88.7 mL, and four ounces is about 118.3 mL (US). The table below shows conversions around 3.4 oz for both US and Imperial volumes:

Volume (fl oz)	US (mL)	UK (mL)
3.0	88.72	85.24
3.4	100.55	96.60
4.0	118.29	113.65

Understanding Fluid Ounces

A fluid ounce measures volume, not weight. Merriam-Webster notes that a US fluid ounce is 1/16 of a US pint, whereas an Imperial (UK) fluid ounce is 1/20 of an Imperial pint. In contrast, a common ounce (oz) is a unit of weight (mass) equal to about 28.35 grams. Mixing them up causes errors (e.g. liquid vs. dry). In metric terms, 1 US fl oz = 29.57 mL, while 1 Imperial fl oz = 28.41 mL. For labeling simplicity, US nutrition labels often treat 1 fl oz as exactly 30 mL. Be careful: using the label value (30 mL) instead of 29.57 mL makes small rounding errors (3.4 fl oz would become 102 mL instead of 100.55 mL).

Defining the Milliliter

A milliliter (mL) is a metric unit of liquid volume equal to one-thousandth of a liter(exactly 1 cubic centimeter). It’s widely used in science, medicine, industry, and food—especially outside the U.S. Today about 95% of the world’s population lives in metricated countries, so milliliters are a standard volume measure globally. In travel and manufacturing, liquid volumes (like water, milk, or shampoo) are commonly given in milliliters.

Understanding that 3.4 oz equals 100.55 mL (US) simply means translating between the customary and metric systems.

Step-by-Step Conversion Formula

Follow these steps to convert fluid ounces to milliliters:

1. Use the conversion factor. In the US system, 1 fl oz = 29.5735 mL. Thus the formula is:
   mL=fl oz×29.5735.
2. Convert the value. Multiply 3.4 fl oz by 29.5735:
   3.4 × 29.5735 = 100.550 mL. (So 3.4 US fl oz ≈ 100.55 mL.)
3. Imperial fluid ounces (UK): If converting from the older Imperial system, use 1 imp fl oz = 28.4131 mL. For example, 3.4 × 28.4131 = 96.605 mL (Imperial).

In short, multiply US fluid ounces by ~29.57 to get mL, or by ~28.41 for Imperial ounces.

Travel Context: TSA’s 3-1-1 Rule

When flying, remember the TSA “3-1-1” liquids rule: carry-on liquids must be in containers 3.4 oz (100 mL) or smaller. Each passenger may bring one clear quart-sized bag of these containers. This rule was instituted after a 2006 security plot, and it aligns U.S. limits with the international standard of 100 mL. In practice, it means any gel, lotion, or liquid (toothpaste, shampoo, perfume, etc.) must fit in those small bottles. Packing bottles larger than 3.4 oz/100 mL will result in them being thrown out at security.

To comply, use travel-sized bottles or decant your products. Buy reusable travel bottles that are labeled 100 mL (3.4 oz), or pour your shampoo, lotion, and even cooking oils into small leak-proof containers. Label each one, seal them in your quart bag, and you’ll sail through the TSA check. Many travelers even keep a dedicated travel kit with 100 mL (3.4 oz) marked bottles, so they never have to measure at the airport. These tips save money and hassle—no more reaching for hotel trial sizes or wasting expensive liquids.

Cooking & Recipe Applications

Converting 3.4 oz in the kitchen is a concrete example of recipe adaptation. For instance, 8 US fl oz (about 1 cup) of milk is roughly 250 mL, and 5 fl oz is ~150 mL. In this light, 3.4 fl oz of milk or water would be 100.55 mL, just under half a cup. Using the wrong measure can alter texture or taste (too little liquid might dry out a cake, too much can make soup thin).

A practical approach is to use dual-marked tools. Measuring cups or spoons that show both fl oz and mL let you pour directly without mental math. For example, a 1/3-cup cup usually marks “2 fl oz / 60 mL”. Digital kitchen scales (with a volume mode) or smartphone kitchen apps can also convert for you. Having a chart or app open while cooking means you can measure out 100 mL directly instead of thinking “how many ounces was that?” With the right tools, converting recipes between US and metric becomes effortless.

Common Conversion Mistakes

• Mixing up weight and volume: An ounce (oz) usually means weight (≈28.35 g), while a fluid ounce means volume. Confusing them causes big errors. (E.g., 16 oz of flour is about 454 g, not 473 mL!)
• Using 30 mL blindly: Remember that 1 US fl oz is actually 29.5735 mL, not exactly 30. If you always round up, 3.4 fl oz becomes 102 mL instead of 100.55 mL. For rough cooking it’s OK, but in science or accurate recipes it matters. (US nutrition labels round 1 fl oz to 30 mL.)
• US vs. UK confusion: If you’re using an Imperial recipe, note that 1 UK fl oz = 28.41 mL, not 29.57. That ~4% difference means 3.4 UK oz is only 96.6 mL, not 100.5 mL. Always check which system the recipe or label means.

Tools & Apps for Instant Conversion

• ConvertUnits.com and Omni Calculator: Online converters do the math for you. For example, Omni’s fl oz-to-mL converter uses 1 fl oz ≈ 29.6 mL, giving instant results.
• Mobile apps: There are many kitchen and travel conversion apps (e.g. Unit Converter, Kitchen Calculator). They convert volumes, weights, and more.
• Voice assistants: Modern smartphones and smart speakers can do conversions on demand. Simply ask “Hey Siri, how many milliliters is 3.4 ounces?” or “Ok Google, convert 3.4 oz to mL” and get an immediate answer.

These tools are handy when you have no calculator at hand. They ensure your conversion is quick and error-free.

Printable Cheat Sheet

For quick reference, use our cheat sheet PDF (free to download) that covers common conversions (1–16 fl oz). It lists each fluid ounce value and its equivalent in milliliters (both US and UK definitions). For example, it shows 1 fl oz = 29.57 mL (US) and 28.41 mL (UK), up to 16 fl oz = 473.18 mL (US) and 454.61 mL (UK). The sheet also notes common cooking measures (1 cup, ½ cup, etc.) in mL. Print or save this chart and keep it in your kitchen or travel bag. Laminate it if you like – having a quick conversion table on hand can save time and prevent mistakes when cooking or packing.

FAQs

1. Q: How many milliliters are in 3.4 fluid ounces?
   A: In the US system, multiply by 29.5735, so 3.4 fl oz ≈ 100.55 mL. In the older British Imperial system it would be 96.60 mL (1 Imp fl oz = 28.4131 mL).
2. Q: Why does TSA say 3.4 oz if they really mean 100 mL?
   A: The TSA liquid rule allows 100 mL per container. Since 100 mL ≈ 3.4 US fl oz, the rule is often called “3.4 oz” for convenience. It’s the same limit, just expressed in US units.
3. Q: Is an ounce the same as a fluid ounce?
   A: No. A plain ounce (oz) is a unit of weight (~28.35 grams), while a fluid ounce (fl oz) is a unit of liquid volume. Many recipes specify “fl oz” for liquid ingredients to avoid confusion.
4. Q: Why do nutrition labels use 30 mL for 1 fl oz?
   A: US labels round 1 fl oz to 30 mL for simplicity. This is a legal definition for packaging, but it’s slightly higher than the exact value (29.57 mL). For rough cooking it’s fine, but precise measurements should use 29.57 mL per fl oz.
5. Q: How do I convert 3.4 oz to mL in a recipe?
   A: Use the formula (mL = oz × 29.5735) or a converter. For cooking, 100.55 mL is just under 0.43 cups. Many recipes give weights instead, so you might use a kitchen scale (1 fl oz water ≈ 29.6 g). Tools like conversion apps or a calculator can do this instantly.
6. Q: Are there easy tools to convert for me?
   A: Yes – many! Online converters like Omni Calculator can instantly convert any volume (Omni lists 1 fl oz = 29.6 mL). Smartphone apps (unit converters) and voice assistants (Siri/Alexa) can also do it by voice. Simply saying “how many mL in 3.4 oz” will give you the answer without math.

Related Conversions

For context, here are a few related conversions: 1 fl oz ≈ 29.6 mL, 8 fl oz (US) ≈ 237 mL (1 cup), and 16 fl oz (1 pint) ≈ 473 mL. Other useful guides include “Ounces to Grams” (for dry ingredients) and “TSA Rules Explained” for travel tips. Converting between units is a common task, so having a set of trusted reference charts and calculators (like this one) is handy. Bookmark related articles on ounce↔milliliter, ounce↔liter, or ounce↔gram for quick future reference.

Conclusion

In summary, 3.4 US fluid ounces = 100.55 milliliters. This conversion is handy in everyday life: it’s the TSA carry-on limit, it appears when halving cup measurements in recipes, and it bridges US and metric cooking. By using the simple formula (mL = oz × 29.5735) and remembering the special cases (100 mL limit, 30 mL rounding), you can convert accurately in the kitchen or at the airport. Save or print the cheat sheet PDF for quick access, and use the tools mentioned to avoid any guesswork. With these tips, you’ll never be caught off-guard by ounces vs. milliliters again. Happy converting!