From ancient standards to modern scientific constants, explore the definitions and histories of the units that measure our world.
The base unit of electric current in the International System of Units (SI).
A unit of land area used in the US and UK systems, equal to 43,560 square feet.
A metric unit of pressure, exactly equal to 100,000 pascals. Roughly equal to atmospheric pressure at sea level.
The most basic unit of information in computing and digital communications.
A unit of digital information typically consisting of eight bits.
The SI base unit of luminous intensity; that is, luminous power per unit solid angle emitted by a point light source.
A scale and unit of measurement for temperature. Zero degrees is the freezing point of water, and 100 is the boiling point (at standard pressure).
A temperature scale primarily used in the United States. 32°F is the freezing point of water, and 212°F is the boiling point.
A metric unit of mass equal to one one-thousandth of a kilogram.
The unit of frequency in the International System of Units (SI), defined as one cycle per second.
The SI unit of energy, equal to the work done by a force of one newton acting through one meter.
The base unit of temperature in the SI system. It is an absolute scale where 0 K is absolute zero.
The base unit of mass in the SI system, now defined by the Planck constant.
The base unit of length in the SI system, defined as the distance light travels in a vacuum in 1/299,792,458 of a second.
The SI base unit for the amount of substance, containing exactly 6.02214076×10²³ elementary entities.
The SI unit of force. It is equal to the force that would give a mass of one kilogram an acceleration of one meter per second squared.
The SI unit of electrical resistance, named after Georg Simon Ohm.
The SI derived unit of pressure used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength.
The base unit of time in the SI system, defined by the transition frequency of the caesium-133 atom.
The derived SI unit of magnetic flux density.
The SI unit of electric potential, electric potential difference, and electromotive force.
The SI unit of power, equivalent to one joule per second.
Now that you know the definitions, use our fast and accurate tools to convert between these units.
