Specific Gravity Calculator

Created by Steven Wooding
Reviewed by Dominik Czernia, PhD and Jack Bowater
Last updated: Feb 02, 2023

The specific gravity calculator determines the relative density of a substance compared to cold freshwater; very useful for knowing if a material floats or sinks or for estimating the amount of alcohol in your homebrewed beer. Of course, if you are an amateur brewer dedicated to your craft, you may find our ABV calculator useful too.

Read on to learn how to find specific gravity by providing the specific gravity formula, explore what specific gravity is, and compare specific gravity vs. density.

You may also visit our density conversion calculator to learn more about the weight to volume ratio of a substance in different units or our API gravity calculator if you are interested in the heaviness of crude oil compared to water.

Specific gravity definition and the specific gravity equation

Specific gravity (also referred to as relative density) is the ratio of the density of a material compared to the density of water at $4\ \mathrm{\degree C}$ ($39.2\ \mathrm{\degree F}$). People usually choose that temperature as it is when water is at its densest. The specific gravity equation is:

$\small \mathrm{specific\ gravity}\! =\!\frac{\mathrm{material\ density}}{\mathrm{water\ density}}$

Since the specific gravity formula consists of one density divided by another, the specific gravity units don't exist. It is a unitless quantity, like most ratios in physics.

Specific gravity values are usually given at one atmosphere of pressure (1013.25 kPa). Remember, that you have to check the temperature of both the material and the reference (usually water) when quoting specific gravities. Standard temperatures vary depending on industry and the material you are measuring.

The specific gravity of water has a value of $1$, as it's being compared to itself, and the same number divided by itself is $1$.

The difference between density and specific gravity is that density is an absolute quantity (mass per unit volume). In contrast, specific gravity compares the density of a material to the density of cold freshwater, and is a relative quantity.

How to calculate specific gravity? - specific gravity vs density

Now that you know what specific gravity is, here's how to find the specific gravity of a substance. Lookup the density of your sample material (or calculate it using our density calculator), then it divide by the density of freshwater at $4\ \mathrm{\degree C}$, which is $1000\ \mathrm{kg/m^3}$ ($62.428\ \mathrm{lb/ft^3}$).

Let's practice by finding the specific gravity of ice, which has a density of $916.7\ \mathrm{kg/m^3}$ ($57.23\ \mathrm{lb/ft^3}$). To do that, we use the specific gravity formula:

specific gravity of ice = 916.7 / 1000 = 0.9167

$\small \mathrm{ice}_{\mathrm{specific\ gravity}}\! =\!\frac{916.7}{1000}= 0.9167$

And that's how to calculate specific gravity. Note that you'll get the same result whatever units of density you use, as long as they are both the same. Give it a go!

How to use the specific gravity calculator?

The specific gravity calculator is straightforward to use, as it requires only one variable to provide. Nevertheless, if you struggle understanding it, then read the following instruction:

1. Enter the density of the substance of interest into the first row of the calculator.
2. The specific gravity will then be shown in the second row (you can't see specific gravity units because it's unitless).
3. The calculator will then tell you whether the material will float, sink, or be neutrally buoyant in cold freshwater.

We've also included some examples of specific gravities of common materials that you can quickly lookup.

You can also use the calculator in reverse, so it becomes a specific gravity to density calculator. Enter a value into the specific gravity row first, to show the density of the material.

FAQ

Are specific gravity and relative density the same thing?

Yes, specific gravity is a slightly outdated way to refer to relative density. Both are quantities that express the density of a substance compared to the one of a reference substance, which is usually water.

How do I calculate the specific gravity of a substance?

To calculate the specific gravity of a substance, follow these easy steps:

1. Isolate a known volume of the substance: V.
2. Use a scale to measure the mass of that volume: m.
3. Calculate the density of the substance with the ratio: ρ = m/V.
4. Choose your reference substance and calculate its density: ρr = mr/Vr
5. Calculate the ratio between the densities: sg =ρ/ρr.

The answer is the specific gravity of the substance.

Why do we use water as a reference when calculating the specific gravity?

Water is often used as a reference when calculating the specific density, mainly due to its omnipresence.

The specific gravity, for example, gives you a quick indication of the buoyancy of an object: if it's greater than 1, the object will sink; if it's smaller than 1, the object will float.

Nothing stops you from computing the specific density using different reference substances!

What is the specific density of mercury?

The specific gravity of mercury is 13.574 (using water as a reference).
To calculate the specific gravity of mercury, you need to follow a couple of steps:

1. Take a volume of mercury, say V = 10 mL.
2. Measure the mass of the volume: m = 135.34 g.
3. Measure the density of mercury: ρ = m [g]/V [cm³] = 135.34 g/ 10 cm³ = 13.534 g/cm³.
4. Take the density of water: ρw = 0.997 g\cm³.
5. Compute the ratio ρ/ρw: sg = ρ/ρw = 13.534/0.997 = 13.574.
Steven Wooding
Density
lb/cu ft
Specific gravity
Example specific gravities
Substance
Water
Specific gravity
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