Does 100ml equal 4 ounces?

When it comes to measuring liquid volumes, it can be confusing converting between metric units like milliliters (ml) and imperial units like fluid ounces (oz). A common question that arises is whether 100ml is equal to 4oz. The short answer is no, 100ml does not exactly equal 4oz. However, the volumes are close enough that they are sometimes used interchangeably in recipes or cooking. In this article, we’ll take a closer look at the metric and imperial systems, how volume units like ml and oz compare, and when it’s reasonable to substitute one for the other.

The Metric and Imperial Systems for Volume

The metric system uses units like milliliters, liters, and cubic centimeters to measure volume. It is the standard system used by scientists, most countries around the world, and even commonly used in the United States in some industries and applications. The base unit of volume in the metric system is the liter.

The imperial system uses units like fluid ounces, cups, pints, quarts, and gallons to measure volume. It originated in the British Empire but is still commonly used in the United States in many everyday applications. The base unit of volume in the imperial system is the gallon.

When measuring volume, units in the metric system relate to each other by factors of 10. For example:

  • 1 liter = 1000 milliliters
  • 1 milliliter = 0.001 liters

Units in the imperial system relate to each other by factors of 2. For example:

  • 1 gallon = 4 quarts
  • 1 quart = 2 pints
  • 1 pint = 2 cups
  • 1 cup = 8 fluid ounces

This makes converting between metric units quite straightforward. Converting between imperial units can be trickier due to the irregular relationships.

Comparing Milliliters and Ounces

So how do milliliters and fluid ounces compare? Let’s look at some key facts:

  • 1 milliliter (ml) is equal to 0.035 fluid ounces (oz).
  • 1 fluid ounce is equal to 29.57 milliliters.
  • 100 ml is equal to 3.38 oz.
  • 4 oz is equal to 118.29 ml.

As you can see, 100ml is close to 4oz but not an exact match. To be precise:

  • 100 ml = 3.38 oz
  • 4 oz = 118.29 ml

The imperial and metric systems have different base units, so conversions will always be approximations rather than exact. But in some cases, like 100ml and 4oz, the volumes are close enough that they can be reasonably interchanged depending on the circumstances.

When is it Acceptable to Substitute 100ml for 4oz?

For scientific applications or situations where precision is critical, you should always convert between metric and imperial units carefully and not assume that 100ml = 4oz. But in everyday cooking or scenarios where approximating the volume is acceptable, it’s generally fine to treat 100ml and 4oz as equivalent.

Here are some examples where substituting 100ml for 4oz will work:

  • Recipes – In baking recipes or other cooking applications, a slight variance in volume of a few tablespoons won’t make a noticeable difference in the outcome. As long as you aren’t drastically altering the proportions of ingredients, substituting the volumes is unlikely to impact the recipe.
  • Measuring out water or other drinks – When measuring out water, juice, milk, or other potable liquids for drinking, the small difference between 100ml and 4oz is imperceptible. Using one instead of the other will result in effectively the same volume.
  • Approximate serving sizes – If you are measuring foods by volume as an approximate serving size guidance, the amounts are close enough to be used interchangeably. The human eye won’t be able to discern 3.38oz from 4oz on a plate or in a bowl.

On the other hand, here are some examples where it’s better to precisely convert between 100ml and 4oz:

  • Medicine dosages – For measuring out cough syrup, prescribed amounts of liquid medication, or other health applications, the slight variance between 100ml and 4oz matters and could impact the potency. Precise conversion is a must.
  • Chemistry experiments – In chemistry labs where reactions may depend on exact fluid volumes, 100ml cannot be assumed to equal 4oz. Proper conversion between units is critical.
  • Nutritional tracking – For calorie counting or nutrition tracking purposes, you’ll want to use the true converted amounts to get accurate measurements for carb, protein, and fat counts.

Converting Between 100ml and 4oz

When you do need to precisely convert between 100ml and 4oz, use the following simplified steps:

  1. Remember that 1 fluid ounce = 29.57 ml.
  2. To convert milliliters to ounces:
    • Divide the milliliters by 29.57
    • For example, to convert 100ml: 100 / 29.57 = 3.38oz
  3. To convert ounces to milliliters:
    • Multiply the ounces by 29.57
    • For example, to convert 4oz: 4 * 29.57 = 118.29ml

You can also use online converters or conversion calculators to easily convert between any imperial and metric volume units. This can be helpful for more complex conversions or large batches.

Quick Conversions

For quick reference, here are some common conversions between 100ml, 4oz, and other volume units:

Metric Volume Imperial Volume
100 ml 3.38 oz
4 oz 118.29 ml
100 ml 0.21 cups
1 cup 236.59 ml
250 ml 1 cup
15 ml 1 tablespoon
5 ml 1 teaspoon


While 100ml does not exactly equal 4 ounces, the volumes are close enough approximations to be reasonably interchanged depending on the use case. For everyday applications like cooking, the small discrepancy between 100ml and 4oz won’t make a significant difference. But for scientific, medical, or technical uses, you should always precisely convert between metric and imperial units. Knowing when it’s acceptable to substitute one for the other comes down to the level of accuracy required for the situation.

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