Physics and chemistry symbols
The constants, units and notation of physics and chemistry, from ħ, c and G to K, mol and eV, ∂, the vector arrow, element symbols and reaction arrows, and what each one stands for.
Test yourself: Physics and chemistry symbols quiz
Constants 5 symbols
Notation 4 symbols
Chemistry and decay 3 symbols
About physics and chemistry symbols
Physics and chemistry use a small alphabet of their own. Some symbols are constants, numbers of nature with a fixed letter: c, the speed of light, and e, the elementary charge, are two of the seven constants on which the BIPM’s SI Brochure now defines every unit. Some are unit symbols, which are easy to get wrong because case and spacing matter: K for the kelvin takes no degree sign, and cd, the candela, is not Cd, cadmium. The rest is notation: marks above or around a letter that change what it means, like the arrow of a vector, Newton’s dot, or the reaction arrows of a chemical equation. Each page here says what one symbol stands for, where it is met, and what it is most often confused with. They draw on NIST’s Guide for the Use of the SI and its tables of physical constants, the BIPM’s SI Brochure, the IUPAC Green Book (Quantities, Units and Symbols in Physical Chemistry) and OpenStax’s free physics and chemistry textbooks, published by Rice University.
Italic or upright
The slope of a letter is part of the symbol. NIST’s guide says symbols for quantities are printed in italic and symbols for units upright, and the Green Book says the same of element symbols, which are always upright. So an italic g is the acceleration due to gravity and an upright g is the gram; an italic A is an area and an upright A the ampere; the italic e is the elementary charge and the upright e the number 2.718….
Greek letters and maths signs
Many of the symbols in a physics formula are Greek letters, and they have their own pages in Greek letters: λ for wavelength and the decay constant, μ for micro, Ω for the ohm, Δ for a change and ∇, the nabla or del, among them. The signs of ordinary arithmetic, such as ≈ and ±, are in Math symbols.
Sources
- The International System of Units (SI), 9th edition, SI Brochure, 9th edition (2019), updated 2024, Bureau International des Poids et Mesures (BIPM), Sec. 2.2 Definition of the SI
- Chemistry 2e, 1.4 Measurements, OpenStax (Rice University), Temperature
- Quantities, Units and Symbols in Physical Chemistry (the Green Book), IUPAC Green Book, 3rd edition, 2nd printing (2008), International Union of Pure and Applied Chemistry (IUPAC), Sec. 2.10.1 (i); Sec. 6.2
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811 (2008), National Institute of Standards and Technology, Sec. 10.2; Sec. 10.2.2
- University Physics Volume 1, 2.1 Scalars and Vectors, OpenStax (Rice University), Scalars and Vectors
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research