The outermost planet of our solar system is Neptune and orbits at a distance of 30 AU (Astronomical Unit - the average distance between the Earth and the Sun - 149,597,870,700 metres).
In terms of the planets, our solar system is 60 AU across. The actual solar system is far bigger than this, with dwarf planets orbiting at thousands of AUs and the Oort cloud (the realm of icy comets) hundreds of thousands, halfway to our nearest star.
1 light year is equal to exactly 9,460,730,472,580,800 metres , so 63,241 AU.
Our planetary solar system is 60 AU across, so approximately 1/1,000th of a light year, and the Oort Cloud 2,000 times larger — around 2 light years across.
Our galaxy, the Milky Way is estimated to be around 100,000 light years in diameter, and 1,000 light years thick generally, increasing to 10–16,000 light years across the central bulge.
Therefore the Milky Way is 100,000,000 (a hundred million) times larger than our planetary solar system, and 50,000 times larger than our total solar system.
The observable universe is estimated to be 93,000,000,000 (93 billion) light years across. It has been around for just 13.8 billion years, but has been constantly expanding, so the farthest reaches of it that we can still see are now 46.5 billion light years from us. Beyond this distance, the light from galaxies can never reach us as they’re moving away faster than the speed of light.
Therefore the Universe (that we can still see) is 930,000 times larger than our galaxy, 47,000,000,000 (47 billion) times larger than our total solar system, and 93,000,000,000,000 (93 trillion) times larger than our planetary solar system.
It can be very difficult to visualise magnitudes of these scales, but using a scale model helps.
Using a scale factor of 1:1,000,000,000 (1 to a billion) we will shrink the Earth down to the size of a marble, 12.7 mm or 1/2 inch across.
At this scale, Neptune would be orbiting 4.5 km or 3 miles away (and at just 50 mm or 2 inches across, you can see why we couldn’t find it until 1846), the planetary solar system then 9 km across, about the size of a small city, with a 1.4 metre (4.6 ft) wide Sun in the centre.
The Oort cloud would be around 20,000 km across, so nearly twice as big as the actual Earth.
This scale doesn’t really help beyond the size of the solar system, as the Milky Way would then be 950,000,000 km across, in between the size of Jupiter and Saturn’s orbits, and the Universe is still 93 light years across!
The problem is if you start with the scale of the Universe as something tangible that can be visualised, such as our planet (most people have been on long distance flights and have a pretty good grasp of how big the Earth is), then the size of our inner solar system becomes tiny.
Let’s shrink the observable universe down to the size of the Earth, so 93 billion light years becomes 12,756 km and we arrive at a scale factor of 1:68,975,222,166,040,639,699 (1 to 69 billion billion). At this scale the Milky Way would be just 13.7 metres or 45 ft across, which happens to be precisely the length of a standard shipping container.
The total solar system including the vast Oort cloud would then just be 0.27 mm or 1 hundredth of an inch across, with Neptune’s orbit just 65 nanometres across, less than the size of an Influenza virus!
The Earth then, at this scale, where the whole observable universe is the size of the actual Earth, would be just 18.5 picometres across, just beyond the resolution of the world’s most powerful electron microscope (20 pm), and half the covalent radius of a hydrogen atom (37 pm).
If the observable Universe was reduced to the size of the Earth then the Milky Way would be the size of a shipping container, the planetary solar system the size of a flu virus and the Earth one quarter the size of a hydrogen atom.