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ChemSpider is a free chemical structure database from the Royal Society of Chemistry (RSC). It gives access to over 120 million structures, along with their properties and associated information, drawn together from hundreds of data sources into a single online search. For researchers in chemistry, it is a place to look up a compound by name or identifier, find a structure by drawing it, or find candidates by formula or mass.
What It Is
ChemSpider is a search service for small-molecule chemistry. It integrates and links compounds from hundreds of high-quality data sources so that a single search shows the freely available chemical data for a substance. Each record is a compound that can be fully represented by a discrete molecular structure; the compound page shows names and synonyms, database identifiers, physical properties and links to the data sources behind the record.
Who Runs It and What It Covers
Since 2009, ChemSpider has been owned by the Royal Society of Chemistry. Its About page states that it works with external partners whose tools enrich the compound records, including the addition of predicted physical properties and 3D structures.
ChemSpider’s help pages define its scope as small molecules: compounds that can be fully represented by a discrete molecular structure. Searches for substances outside that scope always fail, and polymers and oligomers are named among the exclusions. Some smaller biomolecules, such as insulin, are included if they can be represented within the constraints of ChemSpider. For other chemistry resources on this site, see the chemistry stockroom guide.
How to Search and Use ChemSpider
- Run a simple search. From the home page, search by name or identifier. The search looks at the names and identifiers in the database, so enter the identifier alone: “58-08-2” rather than “CAS 58-08-2”, “benzene” rather than “benzene structure”, and a SMILES string without the word “SMILES” in front of it. Extra words such as “reaction” or “melting point” are not understood either.
- Open the structure search. The structure search page is built with the Ketcher editor and the Indigo and Bingo toolkits. It offers three ways to enter a molecule: Draw structure, Convert name to structure, and Load a structure file (.mol).
- Choose a match type. The options are Exact match, Same skeleton, Substructure and Similarity. For similarity searches the thresholds run from 70% or higher to 99% or higher.
- Set the isotope option. Choose Any, Isotopically labeled only or Disregard isotopically labeled.
- Use advanced search for properties. The advanced search page lets you filter by molecular formula, average mass, monoisotopic mass, elemental constraints and specific data sources.
- Open a compound record. Select a result to see its page, which carries the ChemSpider ID, names and synonyms, database IDs and property data. Literature references are often cited with a Crossref DOI.
Strengths and Limits
Strengths
- Wide coverage. More than 120 million structures from hundreds of data sources are searchable in one place.
- Several ways in. You can search by identifier, by drawn structure, or by formula and mass.
- Works with lab records. Identifiers and SMILES strings found on a record can be copied into an electronic lab notebook alongside your own entries.
Limits
- Small molecules only. Polymers, oligomers and other substances that cannot be fully represented by a discrete structure will not be found.
- Strict query format. Descriptive words added to an identifier cause the simple search to miss it.
Alternatives to ChemSpider
PubChem is the best-known open alternative for compound lookup; see our PubChem platform guide for what it holds. Check each database’s own pages for current scope, record counts and access terms.
Programmatic Access and ChemSpider API
The RSC Developer Portal hosts the ChemSpider APIs. They support programmatic searching by chemical name, SMILES, InChI, formula and mass range, and use an API key for authentication. If you are preparing a chemistry manuscript, ChemRxiv is covered in a separate guide.
Frequently Asked Questions
Who owns ChemSpider?
The Royal Society of Chemistry. ChemSpider has been owned by the RSC since 2009.
How many structures does ChemSpider contain?
Its About page states over 120 million structures, with properties and associated information, from hundreds of data sources.
What is the difference between ChemSpider and PubChem?
They are separate databases run by different organisations. ChemSpider is run by the RSC and is limited to small molecules that a discrete structure can represent. For PubChem, read our PubChem guide.
How do I search ChemSpider by drawing a structure?
Open the structure search, choose Draw structure, sketch the molecule in the Ketcher editor, pick a match type (Exact match, Same skeleton, Substructure or Similarity) and run the search. You can instead use Convert name to structure or Load a structure file.
Does ChemSpider have an API?
Yes. The ChemSpider APIs are hosted on the RSC Developer Portal and use an API key.
Why does my ChemSpider search find nothing?
Check that you entered the identifier alone, without words such as “CAS” or “SMILES”, and that the substance is a small molecule. Polymers and oligomers always fail.
Sources
All pages below were checked on 2026-11-07.
- ChemSpider, About: https://www.chemspider.com/about
- ChemSpider, How to search by name: https://www.chemspider.com/help-how-to-search-by-name
- ChemSpider, Structure search: https://www.chemspider.com/StructureSearch
- ChemSpider, Advanced search: https://www.chemspider.com/AdvancedSearch
- Royal Society of Chemistry Developer Portal: https://developer.rsc.org/
