SI prefixes
Units before units
SI prefixes are the standardized prefixes attached to metric units to indicate multiples or fractions of ten.
Larger quantities use kilo- (thousand), mega- (million), giga- (billion), and tera- (trillion).
Smaller quantities use milli- (thousandth), micro- (millionth), nano- (billionth), and pico- (trillionth).
A kilometer is a thousand meters; a millisecond is a thousandth of a second.
SI stands for Système International, the modern metric system.
Trillionth of a meter
- picosecondTrillionth of a second
- picofaradCapacitance unit, trillionth-scale
- picocurieRadioactivity measurement unit
- trillionthDivided by twelve zeros
Ten-liter unit
Metric length unit
- centigramMetric mass fraction
- centiliterMetric volume unit
- centisecondHundredth of a second
- centigradeTemperature measurement system
Thousandth of a meter
- millisecondTiny time unit
- milligramOne-thousandth gram
- milliliterCubic centimeter equivalent
- milliampereCurrent measurement unit
millivolt · milliwatt · millibar · millifarad · thousandth · milliradian · milliohm · millicurie
Metric length unit
Metric unit, billion-fold smaller
- nanosecondOne-billionth second unit
- nanogramBillionth of a gram
- nanoliterOne-billionth liter
- nanowattOne billionth watt
nanomole · nanotechnology · nanoparticle · nanotube · nanoscale · nanorobotics · nanomedicine · nanofiber
Data capacity measure
- megahertzOne million oscillations per second
- megawattMillion-watt unit
- megavoltMillion-volt unit
- megapixelMillion picture elements
megagram · megajoule · megaton · megabit · megapascal · megaohm · megaflop · millionfold
Trillion-byte measure
Millionth of a meter
- microsecondOne-millionth of a second
- microgramMillionth of a gram
- microliterOne-millionth liter unit
- microfaradCapacitance measurement unit
microvolt · microwatt · microampere · micron · microprocessor · microchip · microscope · microbiology
Base unit of mass
- kilometerThousand meters
- kilowattThousand watts of power
- kilohertzThousand-cycle frequency unit
- kilobyteStorage measurement unit
kilovolt · kiloliter · kilopascal · kilojoule · kiloton · kilobase · kilobit · kilocalorie
Data storage unit
- gigahertzFrequency unit, billions
- gigawattBillion-watt unit
- gigavolt10⁹ volts
- gigabitBillion bits of data
gigajoule · gigapascal · gigaflops · gigapixel · billionfold
Quintillionth of a second
- quintillionthOne part per quintillion
- laser pulsesBrief coherent radiation emissions
10⁻¹⁵ meters
- femtosecondQuadrillionth of a second
- femtoliterOne quadrillionth liter
- quadrillionthDivided by ten-to-fifteenth
- atomic nucleiCentral atomic masses
One hundred liters
- hectogram100 grams
- hectare10,000 square meters
- hectopascalMetric pressure unit
- hundredfoldHundred times over
picometer
Trillionth of a meter
- picosecondTrillionth of a second
- picofaradCapacitance unit, trillionth-scale
- picocurieRadioactivity measurement unit
dekaliter
Ten-liter unit
centimeter
Metric length unit
- centigramMetric mass fraction
- centiliterMetric volume unit
- centisecondHundredth of a second
millimeter
Thousandth of a meter
- millisecondTiny time unit
- milligramOne-thousandth gram
- milliliterCubic centimeter equivalent
milliampere · millivolt · milliwatt · millibar · millifarad · thousandth · milliradian · milliohm · millicurie
decimeter
Metric length unit
nanometer
Metric unit, billion-fold smaller
- nanosecondOne-billionth second unit
- nanogramBillionth of a gram
- nanoliterOne-billionth liter
nanowatt · nanomole · nanotechnology · nanoparticle · nanotube · nanoscale · nanorobotics · nanomedicine · nanofiber · nanomaterial
megabyte
Data capacity measure
megapixel · megagram · megajoule · megaton · megabit · megapascal · megaohm · megaflop · millionfold
terabyte
Trillion-byte measure
micrometer
Millionth of a meter
- microsecondOne-millionth of a second
- microgramMillionth of a gram
- microliterOne-millionth liter unit
microfarad · microvolt · microwatt · microampere · micron · microprocessor · microchip · microscope · microbiology · microorganism
kilogram
Base unit of mass
kilobyte · kilovolt · kiloliter · kilopascal · kilojoule · kiloton · kilobase · kilobit · kilocalorie · kilonewton
gigabyte
Data storage unit
gigabit · gigajoule · gigapascal · gigaflops · gigapixel · billionfold
petabyte
Quadrillion bytes measured
- petabitQuadrillion-bit data unit
attosecond
Quintillionth of a second
- quintillionthOne part per quintillion
- laser pulsesBrief coherent radiation emissions
exabyte
Quintillion bytes measurement
femtometer
10⁻¹⁵ meters
- femtosecondQuadrillionth of a second
- femtoliterOne quadrillionth liter
- quadrillionthDivided by ten-to-fifteenth
hectoliter
One hundred liters
- hectogram100 grams
- hectare10,000 square meters
- hectopascalMetric pressure unit
yottabyte
Largest standard storage measure
zettabyte
Sextillion-byte storage unit