How big is that?

1. A proton0.00 pmAbout the size of a proton, far smaller than an atom.
2. A hydrogen atom110.00 pmRoughly a tenth of a nanometre across.
3. A DNA strand’s width2.0 nmThe double helix is about two nanometres wide.
4. A bacterium2.0 µmA typical bacterium is a few thousandths of a millimetre.
5. A red blood cell7.0 µmAbout seven thousandths of a millimetre across.
6. A human hair70.0 µmA hair is near a tenth of a millimetre thick.
7. An ant5.0 mmA small ant, about five millimetres long.
8. A person1.7 mA handy ruler for everything else on this list.
9. A blue whale25 mThe largest animal alive, about 25 metres.
10. The Eiffel Tower330 m330 metres to the tip.
11. Mount Everest8.8 km8,849 metres above sea level.
12. The Earth12,742 kmThe planet’s diameter, about 12,742 kilometres.
13. Earth to the Moon384,400 kmThe average distance, about 384,400 kilometres.
14. The Sun1,392,000 kmThe Sun’s diameter, about 1.39 million kilometres.
15. Earth to the Sun149,600,000 kmOne astronomical unit, about 150 million kilometres.
16. The nearest star4.2 light-yearsProxima Centauri, about 4.2 light-years.
17. The Milky Way100,415 light-yearsOur galaxy’s width, on the order of 100,000 light-years.
18. The observable universe93,016,078,040 light-yearsAbout 93 billion light-years across. A limit on what we can see, not a wall.

These are round figures so the steps stay clear: a typical size, not a measurement of one particular object. The universe figure is the diameter of the observable universe.