Free Specific Gravity Calculator

Understanding Specific Gravity and Its Applications

The specific gravity calculator (also referred to as a relative density calculator) is a practical tool for determining whether a material will float or sink in cold freshwater, for converting density to specific gravity or specific gravity to density, and for comparing the densities of various materials (material density comparison). Whether you are a homebrewer estimating alcohol content or an engineer evaluating material properties, this online tool provides quick insight into buoyancy and relative density.

What Is Specific Gravity?

Specific gravity (or relative density) compares the density of a target substance to the density of pure water at $4\ \mathrm{°C}$ ($39.2\ \mathrm{°F}$), which is the temperature at which water reaches its maximum density. The specific gravity formula is:

$$SG = \frac{\rho_{\text{substance}}}{\rho_{\text{water}}}$$

Because this equation divides one density by another, the result is a dimensionless number—it carries no units. Standard values are usually quoted at one atmosphere of pressure ($1013.25\ \mathrm{hPa}$), and it is important to note the temperatures of both the substance and the reference water when reporting specific gravity.

For water itself, the specific gravity equals $1$, since any number divided by itself yields $1$. This baseline makes it easy to judge relative heaviness: if a material’s specific gravity exceeds $1$, it will sink in freshwater; if it is less than $1$, it will float; if exactly $1$, it is neutrally buoyant.

Specific Gravity vs. Density

Though often confused, density and specific gravity are distinct quantities. Density is an absolute measure of mass per unit volume (e.g., $\text{kg/m}^{3}$ or $\text{lb/ft}^{3}$). In contrast, specific gravity is a relative ratio that compares a substance’s density to that of water. Thus, specific gravity is unitless and directly indicates buoyancy, while density requires a unit and does not immediately tell you if an object floats.

How to Calculate Specific Gravity

To find the specific gravity of a material, first obtain its density (you can measure it or use a density reference). Then divide that density by the density of freshwater at $4\ \mathrm{°C}$, which is $1000\ \text{kg/m}^{3}$ ($62.428\ \text{lb/ft}^{3}$).

For example, ice has a density of about $916.7\ \text{kg/m}^{3}$ ($57.23\ \text{lb/ft}^{3}$). Applying the specific gravity formula:

$$SG_{\text{ice}} = \frac{916.7\ \text{kg/m}^{3}}{1000\ \text{kg/m}^{3}} = 0.9167$$

Because $0.9167 < 1$, ice floats in water. Note that the same ratio is obtained regardless of the units used for density, as long as both densities are expressed in the same unit system.

Using the Specific Gravity Calculator

The calculator is straightforward: enter the density of your substance of interest, and it instantly returns the specific gravity value. It also indicates whether the material will float, sink, or be neutrally buoyant in cold freshwater. For convenience, the tool includes a lookup table of specific gravities for common materials.

The calculator can be used in reverse as well—enter a specific gravity value, and it computes the corresponding density. This makes it a handy density to specific gravity and specific gravity to density converter.

By integrating material density comparison and buoyancy assessment, this relative density calculator serves a wide range of applications, from brewing and cooking to geology and aerospace engineering.