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A Dictionary of Scientific Units Named After People: Newton, Watt, Hertz, Kelvin

From the newton and pascal to the watt, volt, hertz, and kelvin — discover the stories of the scientists behind these familiar units.

Newton (N) — Force and energy units · Isaac Newton

A unit of force named after the British physicist Isaac Newton, who established the law of universal gravitation and the laws of motion. One newton is defined as the amount of force required to give a 1 kg mass an acceleration of 1 m/s².

Pascal (Pa) — Force and energy units · Blaise Pascal

A unit of pressure named after the French mathematician and physicist Blaise Pascal, who discovered Pascal's principle regarding fluid pressure. It is also used in weather-forecast readings for atmospheric pressure (hPa).

Joule (J) — Force and energy units · James Prescott Joule

A unit of energy (work) named after the British physicist James Prescott Joule, who experimentally demonstrated that heat and work can be converted into each other. It is also the basis for the kilojoule (kJ) figure used to express the calorie content of food.

Watt (W) — Force and energy units · James Watt

A unit of power (energy per unit time) named after the Scottish inventor James Watt, who significantly improved the steam engine. It is commonly used to express the power consumption of light bulbs and home appliances.

Volt (V) — Electricity and magnetism units · Alessandro Volta

A unit of voltage (potential difference) named after the Italian physicist Alessandro Volta, who invented the first chemical battery. It is used to express the voltage of batteries or electrical outlets.

Ampere (A) — Electricity and magnetism units · André-Marie Ampère

A unit of electric current named after the French physicist André-Marie Ampère, who studied the relationship between electric current and magnetic fields; it is one of the 7 base units of the International System of Units (SI).

Ohm (Ω) — Electricity and magnetism units · Georg Ohm

A unit of electrical resistance named after the German physicist Georg Ohm, who established the relationship between voltage, current, and resistance (Ohm's law).

Hertz (Hz) — Electricity and magnetism units · Heinrich Hertz

A unit of frequency (the number of repetitions per second) named after the German physicist Heinrich Hertz, who was the first to experimentally prove the existence of electromagnetic waves. It is also used to express radio wave frequencies or computer clock speeds.

Tesla (T) — Electricity and magnetism units · Nikola Tesla

A unit of magnetic flux density (magnetic field strength) named after Nikola Tesla, the Serbian-American inventor (born in what is now Croatia, then part of the Austrian Empire) who made major contributions to the development of alternating-current electrical systems; it is used to express the magnetic field strength of MRI equipment.

Kelvin (K) — Temperature and radioactivity units · Lord Kelvin (William Thomson)

A unit of temperature named after the title of British physicist William Thomson — "Lord Kelvin" — who proposed the concept of absolute temperature. It uses absolute zero (0 K, about −273.15°C), the theoretical lowest possible temperature, as its reference point.

Celsius (°C) — Temperature and radioactivity units · Anders Celsius

A unit of temperature named after the Swedish astronomer Anders Celsius, who proposed a temperature scale based on the freezing and boiling points of water; it is used in everyday life in most countries today.

Becquerel (Bq) — Temperature and radioactivity units · Henri Becquerel

The International System of Units (SI) unit for measuring radioactivity (the number of atomic nuclei decaying per second), named after the French physicist Henri Becquerel, who first discovered natural radioactivity emitted from uranium.

Curie (Ci) — Temperature and radioactivity units · Marie and Pierre Curie

A unit of radioactivity named after Marie Curie and Pierre Curie, the married couple who won the Nobel Prize for their research on radioactivity. It has since been replaced by the SI unit becquerel (Bq), but it is still occasionally used in medical and industrial settings.

Why are units named after people?

The international scientific community, including bodies like the General Conference on Weights and Measures (CGPM), often adopts a unit name derived from the surname of the scientist who first defined a particular physical quantity or discovered a related law, as a way of honoring their contribution. By international convention, the symbol for such a unit is capitalized (for example, N for the newton), but when the unit's full name is spelled out, it is written in lowercase (for example, "newton").

Curious about basic physics laws?

If you're curious about Newton's laws of motion themselves, take a look at our guide to Newton's laws of motion as well.

Frequently Asked Questions

Are all scientific units derived from people's names?

No. Many units, like the meter (m), second (s), and kilogram (kg), are derived from natural phenomena or Greek and Latin words. Units named after people tend to appear most often in physical quantities that were precisely defined relatively late, such as force, pressure, energy, and electricity.

What's the difference between Celsius (°C) and Kelvin (K)?

Both units express temperature, but they use different reference points. Celsius uses the freezing point (0°C) and boiling point (100°C) of water as its reference, while Kelvin is an absolute-temperature unit that uses absolute zero (0 K), the theoretical lowest possible temperature, as its reference.