InChI to InChIKey Converter
In short: Convert full InChI identifiers into compact InChIKey format for search and indexing. It is free, works in your web browser and needs no download.
Convert a full InChI string into the compact InChIKey value.
Input and output formats
| Input: InChI | Output: InChIKey | |
|---|---|---|
| Full name | InChI (IUPAC International Chemical Identifier) | InChIKey |
| What it holds | A layered text identifier built from the structure. The standard InChI is the same in every program. | A 27 character hash of the InChI, made for web and database search. It cannot be turned back into a structure without a lookup database. |
| File or form | Text starting with InChI=1S/ | Text like XXXXXXXXXXXXXX-YYYYYYYYYY-Z |
File Format Explained
InChI is a full layered chemical identifier that can describe connectivity, hydrogens, charge, stereochemistry, and isotope information.
InChIKey is a shorter hashed representation of an InChI. It is easier to search and index, but it is not meant to preserve all structural layers in a readable form.
Use InChI when you need full identifier detail. Use InChIKey when you need a compact database key or search-friendly compound identifier.
InChI versus InChIKey
An InChI is a layered text description of a structure: formula, connectivity, hydrogens, charge, and stereochemistry each sit in their own layer. It is precise but long, and it contains characters such as slashes that search engines handle poorly. The InChIKey is a fixed 27-character hash of the InChI, built for web search and database indexing.
Reading an InChIKey
Aspirin's InChIKey is BSYNRYMUTXBXSQ-UHFFFAOYSA-N.
- The first block of 14 letters encodes the connectivity (the molecular skeleton).
- The second block of 10 characters encodes stereochemistry, isotopes, and other layers, plus flags for the standard InChI and version.
- The final letter encodes protonation; N means neutral.
FAQ
Can I convert an InChIKey back to a structure? Not mathematically, because a hash cannot be reversed. You need a database lookup, which is what the InChIKey to InChI tool does. Can two molecules share an InChIKey? Collisions are possible in theory but extremely rare in practice. Stereoisomers share the first block but differ in the second.
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