The same lower-case letter, claimed by a constant and by a multiplier of a thousand.
Look at what follows. A prefix never stands alone — it is glued to a unit symbol, as in kW or kg. A constant stands by itself in an equation. Careful physical writing subscripts the constant as k_B for exactly this reason, and the kelvin's capital K is a third claimant to the same letter.
Both are a bare lower-case k, and both appear in physical formulae.
| Boltzmann constant symbol | Kilo prefix symbol | |
|---|---|---|
| What it is | A physical constant | A multiplier of one thousand |
| Stands alone? | Yes | No — always before a unit |
| Careful form | Subscripted as k_B | Bare k, always lower case |
| Also claimed by | Spring and rate constants | Nothing — but capital K is the kelvin |
| Relationship (from Symbolwise's records) | Commonly confused with Kilo prefix symbol — Both are a bare lower-case k, and both appear in physical formulae. | Commonly confused with Boltzmann constant symbol — A third claimant to the letter k, alongside the kelvin. |
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for origin narrative and for units the SI does not define, never for an official-definition claim.
CODATA Internationally Recommended Values of the Fundamental Physical Constants
NIST / CODATA Task Group on Fundamental Constants · retrieved 2026-08-01
Authoritative for the recommended value and uncertainty of a physical constant, and for whether that value is exact by definition or measured. It fixes values; it does not decide which letter denotes which quantity, and no record cites it for a symbol's meaning.
A capital K is the kelvin, a unit of temperature. A lower-case k is the prefix kilo, meaning a factor of one thousand and never standing alone. So kW is a kilowatt and KW is not a real unit symbol at all. NIST's guide lists exactly this kind of case error among the standard mistakes in applying the SI.
Alpha is a Greek letter and stands for a quantity — an angle, a coefficient, a significance level. The proportionality sign is an operator and stands between two quantities to say they keep a constant ratio. The drawings differ in that the proportionality sign's right-hand stroke runs out in an open curve rather than closing into the letter's tail.
The becquerel counts nuclear decays — one per second — and says nothing about harm. The sievert weights absorbed energy by the kind of radiation delivering it, and so estimates biological effect. A becquerel of one isotope and a becquerel of another can carry very different risk, which is exactly why exposure limits and medical doses are stated in sieverts and never in becquerels.
Equal-length lines mean a capacitor. Alternating long and short lines mean a battery, with the long line positive. If the second line is curved rather than straight it is a polarised capacitor — still a capacitor, but one that must be fitted the right way round.