10 Best Chemistry Databases of 2026

1. 1

   PubChem

   The NIH's free public database of chemicals, their properties, biological activities, safety data, patents and literature.

   9.5overall

   The NIH's free public database of chemicals, their properties, biological activities, safety data, patents and literature.

   Best forStudents, teachers and researchers who want one free place to look up almost any compound.

   Adoption data

   millionsThe PubChem team at NCBI reports in its 2025 update paper that the database is visited by millions of users every month.

   National Center for Biotechnology Information (Nucleic Acids Research), PubChem 2025 update (2024): “Visited by millions of users every month (see Figure 1 ), it serves as a key information resource for the scientific community as well as the general public.”

   PubChem is the answer for most people asking where to look up a chemical. Run by the National Center for Biotechnology Information at the U.S. National Library of Medicine, it describes itself as the world's largest collection of freely accessible chemical information. Its 2025 update paper counts 119 million compounds, 322 million substances and 295 million bioactivities from 1.67 million assay experiments, gathered from more than 1,000 data sources. You can search by name, formula, structure or identifier and land on a compound page with properties, safety and toxicity information, patents and literature citations. Recent additions include a consolidated literature panel that merges every reference for a compound into one exportable list and a patent knowledge panel that shows what is co-mentioned with a chemical in patents. The trade-off is that PubChem aggregates rather than curates everything itself, so values can differ between depositors, and it is not built for planning syntheses. For that, a licensed SciFinder or Reaxys seat goes further.

   Strengths

   • +Completely free with no account needed
   • +119 million compounds and 295 million bioactivities as of September 2024
   • +Pulls together safety, literature and patent data on one compound page

   Limitations

   • −Aggregated data quality varies by depositor
   • −Reaction search is far thinner than SciFinder or Reaxys
   • −The volume of sections on a compound page can overwhelm beginners

   SummaryPubChem is the best chemistry database for most users because it is free and covers properties, safety, bioactivity, literature and patents for over 100 million compounds. Add SciFinder or Reaxys only when you need curated reaction data.

2. 2

   CAS SciFinder

   The American Chemical Society's curated research platform for substances, reactions, literature and patents, built on CAS REGISTRY.

   8.5overall

   The American Chemical Society's curated research platform for substances, reactions, literature and patents, built on CAS REGISTRY.

   Best forGraduate researchers and industry chemists at institutions that license it and need the most complete substance and reaction coverage.

   CAS SciFinder is the database many chemistry departments and R&D labs treat as the reference of record. It sits on top of CAS REGISTRY, which CAS says contains more than 300 million disclosed substances curated from the literature and other sources, and it is the home of the CAS Registry Number used across regulation and commerce. CAS describes searching by structure, name, CAS Registry Number or spectra data, then moving to related literature, patents and regulatory information. Its retrosynthesis tools mix curated real-world reactions with a predictive model and let you tailor routes for cost, selectivity or speed, and supplier data helps you source what you plan to make. AI-assisted search tools sit on top. The drawbacks are about access rather than content: CAS publishes no price, sells mainly to institutions, and limits academic accounts to academic research. If your library already pays for it, it is the strongest tool on this list; if not, PubChem covers most everyday lookups for free.

   Strengths

   • +Built on CAS REGISTRY, which CAS says holds 300+ million substances
   • +Curated by CAS scientists rather than aggregated
   • +Retrosynthesis and sourcing in the same platform

   Limitations

   • −No public price; access usually comes through an institution
   • −Academic licenses limit use to academic research
   • −Overkill for quick property lookups that free databases cover

   SummarySciFinder has the deepest curated substance and reaction coverage here, backed by CAS REGISTRY. It ranks second only because it is sold by institutional license with no public price.

3. 3

   Reaxys

   Elsevier's chemistry database of experimental properties, reactions and literature, with AI search and predictive retrosynthesis.

   8.4overall

   Elsevier's chemistry database of experimental properties, reactions and literature, with AI search and predictive retrosynthesis.

   Best forSynthetic and medicinal chemists who want experimental reaction conditions and property data, often as an alternative or complement to SciFinder.

   Reaxys is the main rival to SciFinder and the one many synthetic chemists prefer for experimental detail. Elsevier says it holds over 500 million searchable experimental properties, including 72 million chemical reactions, plus more than 100 million literature records from 16,000 periodicals. Reaction records include excerpted conditions such as solvents, catalysts and yield, which is what you need when repeating a procedure rather than just identifying a compound. Newer features include natural language AI search over journals and patents and predictive retrosynthesis. Elsevier also pitches Reaxys for teaching, listing undergraduates, graduate students, PhD candidates, postdocs and professors as academic users, and offers the free ReactionFlash app with over 1,000 named reactions. As with SciFinder, there is no public price; universities and companies license it through Elsevier sales. Many libraries hold one or the other, so check which your institution provides before deciding.

   Strengths

   • +Deep experimental property and reaction condition data
   • +Strong teaching material for higher education
   • +Free ReactionFlash app for learning named reactions

   Limitations

   • −No public price list
   • −Access usually depends on an institutional subscription
   • −Substance identity coverage is narrower than CAS REGISTRY

   SummaryReaxys is the best choice for experimental reaction conditions and property values. Like SciFinder, it is only realistic through an institutional license.

4. 4

   ChemSpider

   The Royal Society of Chemistry's free chemical structure database that links out to hundreds of data sources.

   8.3overall

   The Royal Society of Chemistry's free chemical structure database that links out to hundreds of data sources.

   Best forStudents and chemists who want a quick free structure, name and identifier lookup with links to original sources.

   ChemSpider is the Royal Society of Chemistry's free structure database, and the RSC describes it as holding over 120 million chemical structures, properties and associated information drawn from hundreds of sources. Its search box accepts systematic names, synonyms, trade names, registry numbers, SMILES and InChI strings, and there are structure and advanced search modes plus filters for single or multi-component structures and isotopically labeled compounds. Records add properties and related information and link back to the original data sources, which helps when you need to trace where a value came from. That makes it a useful second opinion next to PubChem, especially for resolving a confusing name or synonym. It is lighter than PubChem on bioactivity, safety and patent data, has no reaction search, and carries advertising and sponsor placements. For a free identifier and structure check it does the job well; for anything deeper, PubChem or a licensed database goes further.

   Strengths

   • +Free from a chemistry society
   • +Over 120 million structures
   • +Accepts many identifier formats in one box

   Limitations

   • −Less bioactivity and safety depth than PubChem
   • −Shows advertising and sponsor content
   • −No reaction search

   SummaryChemSpider is a solid free structure and identifier lookup with links to its sources. PubChem covers more ground for the same price.

5. 5

   NIST Chemistry WebBook

   NIST's free Standard Reference Database 69 of evaluated thermochemical, spectral and physical property data.

   8.3overall

   NIST's free Standard Reference Database 69 of evaluated thermochemical, spectral and physical property data.

   Best forPhysical chemists, engineers and students who need trustworthy thermochemistry, IR and mass spectra or fluid property data.

   Adoption data

   two millionNIST reports that the Chemistry WebBook receives more than two million page views per month.

   National Institute of Standards and Technology, NIST Chemistry WebBook project page (2026): “The NIST Chemistry WebBook receives more than two million page views per month.”

   The NIST Chemistry WebBook is where you go when a number has to be right. It is NIST Standard Reference Database 69, and its home page credits each data collection to the specialists who compiled or evaluated it, from neutral thermochemistry and heat capacities to ionization energies, vibrational frequencies, Henry's law constants and the NIST Mass Spectrometry Data Center's spectra. You can search by name, formula, CAS number, IUPAC identifier or structure, and also by properties such as ion energetics or acidity. The fluid systems section plots thermophysical properties as functions of temperature and pressure. NIST lists it among its free web interface reference databases, and a NIST project page reports more than two million page views per month. The limits are clear in its FAQ: it only includes chemical species for which NIST has data, and it offers no bioactivity, literature or sourcing features. Use it alongside PubChem rather than instead of it.

   Strengths

   • +Free from a national metrology institute
   • +Data compiled and evaluated by named experts
   • +Spectra and thermochemistry that general databases lack

   Limitations

   • −Covers only species for which NIST has data
   • −No bioactivity, supplier or literature search
   • −Older interface

   SummaryThe WebBook is the most trustworthy free source for thermochemistry and reference spectra. Its narrow scope keeps it below PubChem for general lookups.

6. 6

   ChEMBL

   EMBL-EBI's free, manually curated database of bioactive molecules with drug-like properties.

   8.2overall

   EMBL-EBI's free, manually curated database of bioactive molecules with drug-like properties.

   Best forMedicinal chemists, drug discovery researchers and cheminformatics students working with bioactivity data.

   Adoption data

   5thAn independent EMBL-EBI impact report based on a survey of more than 4,000 users ranked ChEMBL as the 5th most used EMBL-EBI resource, as cited in the ChEMBL 2023 paper.

   EMBL-EBI (Nucleic Acids Research), The ChEMBL Database in 2023: a drug discovery platform spanning multiple bioactivity data types and time periods (2021): “A recent independent impact report, derived from a detailed survey of >4000 users, ranked ChEMBL 5th in EMBL-EBI’s most used resources, behind only the much larger and long-established gene and protein sequence databases”

   ChEMBL is the free database to use when the question is what a molecule does in biology. EMBL's European Bioinformatics Institute describes it as a manually curated database of bioactive molecules with drug-like properties that brings together chemical, bioactivity and genomic data. Release 33, described in the 2023 Nucleic Acids Research paper, held more than 20.3 million bioactivity measurements and 2.4 million unique compounds drawn from more than 88,000 publications and patents and 420 deposited datasets. The same paper cites an independent survey of more than 4,000 users that ranked ChEMBL fifth among EMBL-EBI's most used resources. Around the core database sit web services for programmatic access, UniChem for cross-referencing identifiers between databases and SureChEMBL for patent compounds. The data is released under a Creative Commons license, two to three times a year. It is not a general chemistry reference: physical properties and reactions are outside its scope, so pair it with PubChem or the NIST WebBook.

   Strengths

   • +Free under a Creative Commons license
   • +Curated rather than raw aggregated bioactivity
   • +Regular releases, about two to three a year

   Limitations

   • −Focused on bioactive compounds, not general chemistry
   • −Little physical property or reaction data
   • −Best used with some cheminformatics skill

   SummaryChEMBL is the best free source of curated bioactivity data for drug discovery. Its narrow focus keeps it in the middle of a general chemistry ranking.

7. 7

   CAS Common Chemistry

   A free CAS resource with nearly 500,000 common and regulated substances from CAS REGISTRY.

   7.5overall

   A free CAS resource with nearly 500,000 common and regulated substances from CAS REGISTRY.

   Best forStudents, teachers and safety staff who need a quick, authoritative CAS Registry Number for a common chemical.

   CAS Common Chemistry is the free front door to CAS data. CAS describes it as an open community resource with nearly 500,000 chemical substances from CAS REGISTRY, chosen to cover common and frequently regulated chemicals and those relevant to high school and undergraduate chemistry classes. You can search by compound name, SMILES, InChI or CAS Registry Number, and an API is offered for developers. The main reason to use it is to get a correct CAS Registry Number and CA Index Name for a common chemical from the organization that assigns them, without a SciFinder license. The limits are deliberate: it is a tiny fraction of CAS REGISTRY's 300+ million substances, it carries no reactions, literature or bioactivity, and the data is provided under a CC BY-NC 4.0 license, which rules out commercial reuse. CAS points users who need the full collection to SciFinder or its custom data services.

   Strengths

   • +Free, curated CAS data
   • +Authoritative CAS Registry Numbers
   • +Simple interface suited to classrooms

   Limitations

   • −Only a small slice of CAS REGISTRY
   • −Non-commercial license
   • −No reactions, literature or bioactivity

   SummaryCommon Chemistry is the quickest free way to confirm a CAS Registry Number for a common chemical. Its small scope keeps it below the broader free databases.

8. 8

   CRC Handbook of Chemistry and Physics Online

   The online edition of CRC Press's long-running reference tables for chemistry and physics, now in its 107th edition.

   7.4overall

   The online edition of CRC Press's long-running reference tables for chemistry and physics, now in its 107th edition.

   Best forStudents and lab scientists who want vetted physical constants and property tables in one reference.

   The CRC Handbook of Chemistry and Physics is the reference book many chemists learned on, and the online edition carries the same tables in a searchable form. The current release is the 107th edition from CRC Press, part of Taylor & Francis, with Leah R. McEwen as editor-in-chief. Its contents run from the elements and their isotopes, atomic weights and abundances to physical constants, critical constants and dissociation constants of organic compounds, with sections on how the data were evaluated and what changed in each edition. The site adds a chemical search, an interactive periodic table and an archive of earlier editions. Access works through a subscribing institution's network or an individual user account; prices are not published on the site. The format is its strength and its limit: it is excellent for looking up a constant from a vetted table, but it is not a compound database with structures, bioactivity or literature links.

   Strengths

   • +Familiar reference trusted in teaching labs
   • +Data sections with an evaluation discussion
   • +Updated with a new edition each year

   Limitations

   • −No public price
   • −Tables, not a compound-centric database
   • −Limited structure search compared with SciFinder or PubChem

   SummaryThe CRC Handbook online is the classic source for vetted property tables. It ranks lower because access is paid and it is organized as tables rather than records.

9. 9

   SpringerMaterials

   Springer Nature's curated property database for materials science, chemistry and physics, including Landolt-Börnstein.

   7.0overall

   Springer Nature's curated property database for materials science, chemistry and physics, including Landolt-Börnstein.

   Best forMaterials chemists and physicists who need crystal structures, phase diagrams and property data for inorganic solids.

   SpringerMaterials is the chemistry database on this list built for materials rather than molecules. Springer Nature describes it as curated data and tools for research in materials science, physics, chemistry and engineering, and it brings together the Landolt-Börnstein collections with Inorganic Solid Phases, SGTE phase diagrams, polymer thermodynamics, ionic liquids, battery materials and organic-inorganic perovskites. You can search by elemental composition or chemical structure and view interactive crystal structures, data tables and phase diagrams with export options. Updates are substantial: the early access ISP 2027 release adds reports on 15,098 new crystal structures, 18,341 physical property datasheets and 1,124 phase diagrams. Access is through institutions, by username and password or institutional login, and prices are not published. For organic synthesis or drug discovery it adds little over SciFinder, Reaxys or PubChem, but for solid-state and materials chemistry it fills a gap the others leave.

   Strengths

   • +Curated, validated materials data
   • +Regular large data updates
   • +Good visualization of structures and phase diagrams

   Limitations

   • −No public price
   • −Materials focus, light on organic chemistry
   • −Requires institutional access for most users

   SummarySpringerMaterials is the best pick here for inorganic solids and materials property data. Its narrow audience and quote-only pricing keep it near the bottom of a general list.

10. 10

    The Merck Index Online

    The Royal Society of Chemistry's online edition of The Merck Index, with over 12,000 monographs on chemicals, drugs and biologicals.

    7.0overall

    The Royal Society of Chemistry's online edition of The Merck Index, with over 12,000 monographs on chemicals, drugs and biologicals.

    Best forPharmacy, pharmacology and chemistry users who want concise expert monographs on drugs and important chemicals.

    The Merck Index has been a desk reference for more than 130 years, and the Royal Society of Chemistry has updated it since 2013. The online edition holds over 12,000 monographs on chemicals, drugs and biologicals, each with physical, pharmacological and historical information, and the RSC says it is continuously expanded with curated content that highlights only the most relevant literature and patents. You can run a basic search by name, CAS Registry Number or molecular formula, use advanced search, browse monographs and open reference tables. The appeal is editorial: a monograph tells you what matters about a substance in a page, which is faster than reading a sprawling database record. The trade-offs are scale and access. Twelve thousand monographs is a small fraction of what PubChem or SciFinder covers, and the RSC handles access through its sales team without a published price.

    Strengths

    • +Expert-written monographs rather than raw data
    • +Strong on drugs and biologicals
    • +Updated by the RSC since 2013

    Limitations

    • −No public price
    • −Covers thousands, not millions, of substances
    • −No structure-based bioactivity or reaction search

    SummaryThe Merck Index Online is the most readable reference for drugs and key chemicals. Its small scope and quote-only access place it last on a general chemistry list.

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