01
Diameters, not precise boundaries
"Where the Milky Way ends" or "how big the Local Group is" doesn't have a sharp edge — these are commonly cited approximate diameters.
Universe · Question
How big is the universe, really?
Big numbers stop meaning anything after a while. This walkthrough takes it one zoom-out at a time — from your own height to the edge of the observable universe — so each jump in scale stays legible.
Visual model
Eight zoom-outs.
What's simplified
These are round numbers, not exact ones.
02
The universe may be infinite
93 billion light-years is the diameter of the observable universe — the part whose light has had time to reach us. The whole universe could be larger, or infinite.
Scale of the universe · reference
Eight scale steps, spanning about 26 orders of magnitude.
The table mirrors the interactive model above. “Size” means height, diameter, span, or distance depending on what is being compared, so unlike quantities are not mislabeled as diameters.
| Step | Scale | Measure used | Approximate value | Jump from previous step |
|---|---|---|---|---|
| 01 | Human | Height | ~1.7 m | Baseline |
| 02 | Earth | Diameter | 12,742 km | ~7.5 million × |
| 03 | Earth–Moon | Average center-to-center distance | 384,400 km · ~1.28 light-seconds | ~30 Earth diameters |
| 04 | Solar system to Neptune | Approximate orbital span | ~9 billion km · ~60 AU · ~8.3 light-hours | ~23,000 × Earth–Moon distance |
| 05 | Nearest star | Distance to Proxima Centauri | ~4.25 light-years | ~4,500 × solar-system span |
| 06 | Milky Way | Rounded stellar-disk diameter | ~100,000 light-years | ~23,500 × nearest-star distance |
| 07 | Local Group | Approximate group extent | ~10 million light-years | ~100 × Milky Way diameter |
| 08 | Observable universe | Diameter | ~93 billion light-years | ~9,300 × Local Group extent |
Scale questions
What the 93-billion-light-year number actually means.
Q1
How can the universe be 93 billion light-years across if it is about 13.8 billion years old?
Because space expanded while the light traveled. The matter that emitted the oldest light we can observe is now roughly 46 billion light-years away in comoving distance, making the observable region about 93 billion light-years across.
Q2
Is the observable universe the entire universe?
No. “Observable” describes the region from which information has had time to reach us. It is not a measured physical wall, and observations do not tell us the total size of the full universe.
Q3
How much wider is the observable universe than the Milky Way?
Using rounded diameters of about 100,000 light-years for the Milky Way and 93 billion light-years for the observable universe, the observable universe is roughly 930,000 times wider.
Misconception check
Quick check.
Quick check
Go deeper
Keep exploring.
Next in this series →
What is a light-year? ↗
Understand the distance unit used for the final four steps of this scale ladder.
Solar System
Distance scale
Zoom back in and compare planetary distances without compressing them into one diagram.
Galaxy
Milky Way
See where the Sun sits inside the galaxy used in step six.