The following table compares InChI to a few common chemical formats.

Comparison of InChI to other formats
Linearized Yes Yes Yes No No
Unique, canonical Yes No10 Possibly1 No No
Human readable Hardly2 Impossible Easily3 Hardly2 Hardly2
Includes atom coordinates No No No Yes4 Yes4 Length (characters per atom)5 ~2 ~111 1-2 ~50 ~50 Software support (0-1) 0.36 0.112 0.27 18 0.59
  1. SMILES is normally not unique, but has the possibility of a canonical form, that is unique for each structure.
  2. These formats separate the information about atoms and bonds and thus their reading by human requires at least a piece of paper, a pen, some knowledge of the format and a lot of patience.
  3. SMILES was designed to be read and written by humans and is therefor relatively straightforward to read, provided the user knows a few basic principles of the format.
  4. These formats do not require presence of atom coordinates, but usually contain them.
  5. This is just a very rough estimate and may vary significantly, especially for the longer formats.
  6. InChI is gaining support from the software producers and is not understood by most major chemical editors.
  7. A few programs support SMILES.
  8. Molfile is a format supported by most chemical packages.
  9. CML is supported by several chemical programs, but is far less common than Molfile.
  10. For every molecule only one InChIKey is valid, however two molecules may have the same InChIKey – more details here.
  11. InChIKey is fixed length (27 characters). For typical organic molecules its length is around 1 character per atom, but can be as much as 27 characters per atom for single atom molecules. For large molecules the ratio drops near to 0 characters/atom.
  12. InChIKey is very new but we expect it to be supported very soon by all software already having InChI support.