How much of the universe is empty?

This is kind of an interesting question because it really depends on your point of view.

Most of everything is actually empty space, if you consider the atomic scale. You know that an atom is a blob of protons and perhaps some neutrons, and electrons are whirling around this blob somewhere farther away. But the diameter of an electron's orbit is many, many, many times larger than the diameter of a proton. So if you think of a relatively solid substance, like carbon, if you made the nucleus out of twelve tennis balls here on earth, the electrons would have to be much much farther away than the moon, and they would be invisible specks at that scale. So if you think about it, the universe is all pretty much empty, even the parts we consider to be solid.

Another interesting thing is that while we can't measure the mass of everything in the universe, we can look at it and compare things we know about, like our own solar system, with things we can see. And it turns out that what we see doesn't add up with what our equations predict. It seems as if only 20% of the matter in the universe can be seen (and not because it's dark in space, either). There is much, much more matter out there that is absolutely invisible; if you shone a flashlight at it, the beam would pass right through unaffected. This is called "dark matter," and the only way we know it's there is by looking at the gravitational effect it has on the matter we can see.

Further complicating this is that according to Einstein, matter and energy are really just the same thing. So all the "empty space" that we look through to see those distant stars and galaxies isn't empty at all, it's teeming with energy. If you look at it that way there is no place in the universe that's empty.

Almost all of it. Well over 99%.

At large scales, the planets in the solar system are incredibly far apart and all the space in between them is empty. If you shrunk the solar system so that the Sun was the size of a basket ball, Mercury would be smaller than a pea and would orbit 30 feet from that basket ball size Sun. So you have a 30 foot wide spherical volume of space with nothing but one basket ball and one very small pea in it. And the space between the stars is even emptier than that.

At small scales, the inside of a rock is considered solid, but the atoms that it is made from are mostly empty space, because the size of the electrons, protons, and neutrons in each atom only account for a tiny fraction of the size of the atom. In a neutron star the electrons are smashed down into the protons, making them into neutrons, getting rid of all that empty space between the electrons and the nucleus.

But it depends on what you mean by empty. Some people above are saying space is not empty because there are a few atoms in every cubic centimeter everywhere in space. But that is like saying a football stadium with only 5 people in it is not empty. That stadium may not be totally empty, but it is pretty empty; like over 99% empty, right?

The present overall density of the Universe is very low, roughly 9.9 × 10−30 grams per cubic centimetre. This mass-energy appears to consist of 73% dark energy, 23% cold dark matter and 4% ordinary matter. Thus the density of atoms is on the order of a single hydrogen atom for every four cubic meters of volume.

Zero percent.

The Earth's atmosphere doesn't really stop at a certain place and then "space" begins. The air gets thinner as you go up from the surface and the farther from Earth (or the Sun) you get the thinner it is. It gets thinner still if you leave our solar system and even thinner in intergalactic space. But it is always there.

In reality, no volume of space can ever be perfectly empty. A perfect vacuum with a gaseous pressure of absolute zero is a philosophical concept that does not exist in nature.

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Universe is not empty there is always one or another kind of matter or energy present.

Keyur is correct, there are virtual particles in every cubic nanometer in space. If u mean baryons (protons and the like) then that's different

According to the Christian Bible KJV the Spirit World is heavily populated but can only be seen through spiritual eyes so the answer to your question would be 8% to 12%....james the hollow earth man.

95% of the universe is void

Most of it...