CODATA fundamental constants, astronomical values, and rational/irrational math constants — searchable, comparable, and convertible, all in your browser.
Pick 2–4 constants to compare their values, units, and ratios side by side.
Browse up to 100 decimal digits of irrational constants, or search for a short sequence (like a birthday, e.g. 0904) inside them.
Paste symbols or names, one per line (e.g. c, pi, Avogadro) — matches are looked up instantly.
Everyday equations that use these constants, with a worked numeric example.
Multiple choice — match the constant to its correct value.
/ to jump to it), or click a category tab: Universal, Electromagnetic, Atomic & Nuclear, Physico-Chemical, Astronomical, Math (Irrational), Math (Rational), or Conversion Factors.Physical constants use the CODATA 2022 recommended values published by NIST. CODATA reviews and updates these values roughly every four years based on the best available experiments.
Since the 2019 SI redefinition, the speed of light, Planck constant, elementary charge, Boltzmann constant, and Avogadro constant are fixed by definition and carry no uncertainty. Every other constant, like the gravitational constant, is derived from measurement and carries an uncertainty that can shift with future CODATA revisions.
Irrational/transcendental constants like pi, e, and the golden ratio can't be written as an exact fraction and their decimal expansion never repeats. The rational entries are exact fractions, including historical approximations of pi like 22/7 and 355/113, shown for comparison.
The Digit Explorer shows up to 100 decimal digits for supported constants (pi, e, √2, golden ratio) and lets you search for a short digit sequence, like a birthday, within them.
Where a meaningful alternate form exists (for example, energy constants shown in both joules and electronvolts), it's listed in that constant's detail view under Alternate Forms.
No. All lookup, conversion, comparison, and quiz logic runs locally in your browser. Favorites and history are saved only in this browser's local storage.
Yes. Each constant's detail view includes copyable variable declarations for Python, JavaScript, C, and LaTeX, and you can export the full filtered list as CSV or JSON.
Values are shown to the precision listed by CODATA 2022 or standard mathematical references, rounded for display. This tool is for reference and coursework, not metrology-grade calculation — always cite the primary NIST/CODATA source for published work.
All tools are free. If they've saved you time, consider supporting us.