Volume represents the three-dimensional space an object or substance occupies. The milliliter ($\text{mL}$) is the standard metric unit used for measuring volume, particularly for liquids and gases. Understanding how to calculate or convert volumes into milliliters is a fundamental skill in science, cooking, and everyday life. A foundational concept of the metric system is the equivalence between a milliliter and a cubic measurement: one milliliter is exactly equal to one cubic centimeter ($\text{cm}^3$). Calculating volume in cubic centimeters automatically provides the result in milliliters.
Calculating Volume from Dimensions
The most direct way to determine the volume of a regularly shaped object is by measuring its linear dimensions and applying the appropriate geometric formula. This method is useful for objects like boxes, tanks, or cylinders, which have defined, measurable straight edges. Measurements must be taken in centimeters to ensure the resulting calculation yields volume in cubic centimeters ($\text{cm}^3$), which is interchangeable with milliliters.
For a simple rectangular prism, such as a carton or a block, the volume is found by multiplying the length, width, and height. If a box measures 10 centimeters long, 5 centimeters wide, and 2 centimeters high, the calculation is $10 \text{ cm} \times 5 \text{ cm} \times 2 \text{ cm}$, resulting in $100 \text{ cm}^3$. Since $1 \text{ cm}^3$ is equivalent to $1 \text{ mL}$, the volume of the box is $100 \text{ mL}$.
For a cylindrical object, like a can or a pipe, the volume is calculated using the formula $V = \pi r^2 h$, where $r$ is the radius and $h$ is the height. Both the radius (half the diameter) and the height must be measured in centimeters. Squaring the radius and multiplying it by the height and pi ($\pi \approx 3.14159$) yields the volume in $\text{cm}^3$. For example, a cylinder with a radius of $3 \text{ cm}$ and a height of $10 \text{ cm}$ would have a volume of approximately $282.7 \text{ cm}^3$, or $282.7 \text{ mL}$.
Converting Common Units to Milliliters
Translating a volume already measured in a different unit into milliliters relies on fixed conversion factors. Converting volumes within the metric system is straightforward. One liter ($\text{L}$), a larger metric unit, is defined as $1,000$ milliliters, meaning conversion simply involves multiplying the number of liters by $1,000$.
Converting from non-metric units, often encountered in household and kitchen measurements, requires specific conversion factors. For example, a US fluid ounce ($\text{fl oz}$) is equal to approximately $29.57$ milliliters. To convert $8 \text{ fl oz}$ of milk, one multiplies $8$ by $29.57$, resulting in a volume of about $236.56 \text{ mL}$.
Common kitchen implements also have defined milliliter equivalents, though slight variations exist between countries. A standard U.S. teaspoon ($\text{tsp}$) is approximately $4.929 \text{ mL}$, but is often rounded to $5 \text{ mL}$ for nutritional labeling. A U.S. tablespoon ($\text{Tbsp}$) is equal to about $14.787 \text{ mL}$, often rounded to $15 \text{ mL}$ for practical use. Finally, if a volume is measured in cubic inches ($\text{in}^3$), the conversion factor is approximately $16.387$ milliliters per cubic inch.
Using Water Displacement for Irregular Shapes
When an object has an irregular shape, such as a rock or a figurine, its volume cannot be calculated using standard geometric formulas. The water displacement method provides a practical alternative for determining the volume of such solids. This technique is based on the principle that when an object is fully submerged in a liquid, it displaces a volume of liquid equal to its own volume.
To perform this measurement, a container, such as a graduated cylinder or a beaker, is partially filled with water, and the initial volume ($\text{V}_{\text{initial}}$) is recorded in milliliters. The irregularly shaped object is then carefully lowered into the water until it is completely submerged. Once the water level stabilizes, the final volume ($\text{V}_{\text{final}}$) is read from the container’s markings. The object’s volume in milliliters is calculated by subtracting the initial volume from the final volume ($\text{V}_{\text{final}} – \text{V}_{\text{initial}}$).