✧ CHEMICAL SPACE EXPLORER
A JOURNEY FROM MOLECULES TO THE COSMOS · HOW THE COUNTS ARE MADE
The combinatorial chemistry of possibility

How big is chemical space?

Choose the elements. Adjust the maximum molecular size. Watch possible molecular structures multiply — and compare their number with the atoms on Earth, in our galaxy, and across the observable universe.

01 / Choose your elements

Click the elements molecules may contain. Hydrogen is always implicitly available. Dimmed elements are outside the organic estimation model.

As atoms are added, possibilities explode

Vertical scale: log₁₀(number of candidate structures)
Computed (exact + sampled)Extrapolation±2 SE / extrapolation envelopeCosmic milestones
Click the plot to set the atom count. Dots mark computed sizes. There the band is ±2 standard errors of the sampler; beyond the computed range it spans extrapolation assumptions and is not a confidence interval.
Illustrative chemical-space estimate
Log₁₀ candidate structures
Uncertainty range

02 / Maximum number of heavy atoms

Non-hydrogen atoms, up to and including this limit (hydrogen is implicit).

20 heavy atoms
1306090120150
Try the GDB-like preset, then increase the slider past 100 atoms.

Against the cosmic scale

Possible types of molecules versus physical atoms: a comparison of magnitudes, not equal quantities.
What is counted?

Neutral, closed-shell, connected molecules with implicit hydrogens, counted as constitutional isomers (no stereoisomers; resonance forms count once). A molecule must pass basic rules: standard valences, bond orders ≤ 3, GDB-style ring-strain filters (no small-ring triple bonds, cyclopropenes or anti-Bredt alkenes) and heteroatom filters (no O–O, N–O or halogen–heteroatom bonds, enols or hemiacetals). These are candidate structures, not experimentally verified compounds. Read how the counts are made →

How is the number estimated?

Counts come from Chemical Space Explorer. Every molecular graph is generated exactly once (canonical augmentation) and counted exactly up to 6 heavy atoms. Larger sizes, up to 12, are estimated by stratified sampling of the generation tree. Beyond that the curve is extrapolated from the computed growth rate and is illustrative only. It never drops below the exact alkane counts. GDB-13/17/20 are quoted for comparison; they use stricter filters, so they sit below these counts.