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 estimating the amount of alcohol in your homebrew beer.

The article explains how to find specific gravity by providing the specific gravity formula, explores what is specific gravity at all, and compares specific gravity vs. density.

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 °C (39.2 °F). People usually choose that temperature as it is when water is at its densest. The specific gravity equation is:

specific gravity = material density / 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 °C, which is 1,000 kg/m³ (62.428 lb/ft³).

Let's practice by finding the specific gravity of ice, which has a density of 916.7 kg/m³ (57.23 lb/ft³). To do that, we use the specific gravity formula:

specific gravity of ice = 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.

Steven Wooding