About Chemkit

Chemkit is a free, open-web reference library of chemistry calculators and cheat sheets, launched 2026-08-13. It exists because most free chemistry calculators on the open web are either numerically wrong, ambiguous about their units, or ad-plastered to the point of unusability. Every tool here is unit-tested against a canonical textbook worked example before it ships, and every physical constant cites its primary source.

What you can do here

Today the site publishes 18 calculators across the six subdisciplines of an undergraduate chemistry curriculum, along with a growing set of reference cheat sheets and pillar articles. The full index lives on the home page and on the Learn hub.

Editorial process

Every published tool has cleared this pipeline before going live:

1. Primary-source verification. Every constant, pKa, molecular weight, unit-conversion factor, and thermodynamic value is looked up in a primary or tertiary reference (NIST, IUPAC, CRC Handbook, PubChem, Harris QCA, Zumdahl) and cited by name + edition in a comment in the calculator's source code.
2. Unit tests against textbook examples. Each calculator has a Vitest suite that covers (a) a canonical worked example lifted from a named textbook chapter, (b) round-trip conversions across every supported unit, and (c) an explicit set of invalid-input rejections (NaN, negative, zero-divisor).
3. Build-time content validation. Every MDX content page's title (≤ 60 chars) and description (140–155 chars) is enforced by a Zod schema at astro build time; a wrong-length string fails the build.
4. Sig-figs correctness. Rounding happens only at the display layer. Intermediate arithmetic is always full IEEE 754 precision. Users can override the auto-detected sig-fig count.
5. Accessibility. Every calculator is keyboard-navigable, has real <label>s (never aria-label substitutes), announces errors via aria-live, and meets WCAG AA color contrast in both light and dark themes.

Primary sources

The following authorities are the primary references for values used across the site. Individual tools cite the specific chapter or table.

• Physical constants — CODATA 2018 recommended values, published by NIST: physics.nist.gov/cuu/Constants.
• Atomic weights — IUPAC 2021 recommended values (Prohaska et al., Pure Appl. Chem. 94, 573): ciaaw.org/atomic-weights.htm.
• Thermodynamic data — NIST WebBook (webbook.nist.gov) and CRC Handbook of Chemistry and Physics, 97th ed. (2016).
• Acid/base dissociation constants — CRC Handbook 97e for inorganics; Good et al. Biochemistry 5 (1966) 467 for the Good's-buffer series; Harris Quantitative Chemical Analysis 10e (2020) Table 9-2 for the standard undergraduate set.
• Molecular structures & masses — PubChem (pubchem.ncbi.nlm.nih.gov) — every quoted MW cites a CID.
• Nomenclature and IUPAC definitions — IUPAC Gold Book.
• Unit conversion factors — NIST Special Publication 811 (2008 revision) for the SI-derived tables.

A per-tool citation index lives at /methodology so you can trace any specific value back to the paper or handbook it came from.

Corrections

Found a value that disagrees with a primary source, or a bug in a calculator's output? Please email contact@chemkit.org with the tool page, the inputs, what your reference source gives, and the citation. Fixes are usually shipped within 48 hours and are noted in the site's changelog.

What we don't do

• No user accounts, no logins, no gated content.
• No tracking beyond aggregate analytics (Google Analytics 4). We do not sell or share visitor data.
• No advertising placeholders styled to look like calculator outputs. Ads, when live, are clearly labeled and never appear inside a calculator's result panel.
• No AI-generated numerical answers. Every calculator is deterministic math with citations you can verify.

Contact

Corrections, questions, and reference-source suggestions: see the contact page. Privacy details: /privacy.