Well there is a simple experiment you can do to answer your own question. You can probably “ask the internet via google”, but why do that? Instead do an experiment. REALITY is the ultimate arbiter! And an experiment allows us to determine reality.

This is an important lesson. Science is the “belief in the possible ignorance of experts”. What I mean is not that an “expert” should be ignored… in almost all cases TRUE EXPERTS are to be trusted, such as the meteorologists who provide weather forecasts. However, IN THE END, experiment is the ultimate arbiter of the TRUTH.

So density is the mass/volume of an object. First you will require a simple kitchen scale. The first thing to do is to obtain the mass of the egg. I have a little kitchen scale and I can measure the mass in grams or ounces. If you do measure in ounces CONVERT TO GRAMS.

Then to measure the volume you can do this:
Fill a wide cup, say a paper or plastic cup, cup roughly half way with water. Mark the water line with a sharpie. Then CAREFULLY place the egg in NO SPLASH!!… and mark the new height of the water line. The displaced water is the volume of the egg. You can carefully pour water out until the egg plus water line returns to the FIRST (pre egg in the cup) level. So now you can take the water you removed and determine ITS mass. Since the density of water is 1 g/ cubic centimeter you can take that mass of water to be the VOLUME of the egg in cubic centimeters.

Now you have the density= mass of egg/ volume of egg.

Question: does the density of egg change if you first hard boil it?

Answer: NO… neglecting any TINY, TINY changes in volume and assuming no leakage of mass from within the egg to outside (it would be super minor), the mass and the volume has not changed! The density is the same.

HOWEVER, it is easy to determine if an egg is hard boiled or not!!! By experiment!! The density does not change, so THAT is not test.

What changes between a fresh egg and a hard-boiled egg??

The DISTRIBUTION OF mass changes. The act of boiling makes the moment of inertia decrease. This is because when egg white is converted to hard egg white the density increases LESS than when the egg yolk undergoes the liquid to solid conversion. This means that if you spin BY THE SAME FORCE a boiled egg and a non-fresh one, for the same amount of hand spin, the boiled egg will spin faster. This is the principle of the conservation of angular momentum. The mass distribution has changed such that more of the mass of the egg is CLOSER to the spin axis or CENTER of the egg.

So there you have it. Use your creative mind to measure things experimentally and make observations (spin the eggs) and then provide an explanation consistent with Nature. This is the hallmark of a scientist; however the method can be used to solve many, many other issues as well.

According to a previous UCSB Science Line question (“How much salt do we need in water to make an egg float?”), the average density of an egg is 1.031 grams per cubic centimeter. However, every egg is different, and there will be small variations in density.

For comparison, at room temperature (20oC or 68oF), water has a density of 0.998 grams per cubic centimeter (Source: CRC Handbook of Chemistry and Physics). So most eggs will sink in water, as they are (slightly) more dense.

BUT, as eggs get old, a little bit of water evaporates out through the shell and is replaced by air. Since air is much less dense than water, this process lowers the density of the egg. Eventually, the egg density will drop enough that the egg can float in water. So, if you want to check how fresh an egg is, you can test whether it floats or sinks in water. If it is old enough to float, you probably shouldn’t eat it!

Interesting question, and let’s start with the basics: what is density? Density is a physical property of an object (e.g. the egg), and is defined as the mass of the object, often given in grams, (how much egg is there) divided by its volume, often given in cm³ or milliliters, (how much space the egg takes up). Mathematically, this is given as D = m / V, where “D” is density, “m” is mass, and “V” is volume. Therefore, if you know the mass of an object and its volume, you can easily calculate its density.

Now with the basics laid, let’s look at your question, and in particular, the use of the word “egg”. For our purposes, let us assume it means hen eggs (those you usually consume for a hearty breakfast), but the procedure to determine the density for any other egg would be the same. For a quick measure, try putting an egg in a cup of water; it will sink, and indicate that the density of the egg is greater than water (density of water is 1 gram/milliliter) as objects more dense than water will sink in water. As for a more rigorous way to determine the exact density of the egg, place the egg in water, and then add salt to the water until the egg begins to float, specifically the edge of the egg is even with the surface of the water, and this is when the water with salt has the same density as the egg. Finally, weigh the water with salt on a scale to get the mass, determine the volume by using cooking ware that can measure in milliliters, and then divide those numbers, and you have arrived at the density of your breakfast egg.

I tried to do the experiment, but it didn't work very well. My chicken egg weighed 2.0 ounces, which is 56 grams. I put it in a measuring cup and filled to cup to 250 milliliters [mL] with water. When I took the egg out of the water, there were about 190 mL of water left, so the egg's volume was about 60 mL, and its mass was 56 grams [gm]. The density of water is 1 gm per mL, and the density result for my egg was 56 gm per 60 mL, which is less than 1 gm per mL.

With better measurements, an egg is just a tiny bit denser than water. That makes sense, because the egg barely sinks in water.