SI Unit Explorer
Explore the seven SI base units, understand prefix scaling, and instantly convert between systems.
meter
Measures length
A dollar bill is about 156 mm long.
Officially defined in 1983
kilogram
Measures mass
A liter of water has a mass close to 1 kilogram.
Officially defined in 2019
second
Measures time
A hummingbird can flap its wings around 50 times per second.
Officially defined in 1967
ampere
Measures electric current
A phone charger commonly outputs around 2 amperes.
Officially defined in 2019
kelvin
Measures thermodynamic temperature
Room temperature is roughly 293 kelvin.
Officially defined in 2019
mole
Measures amount of substance
One mole contains exactly 6.02214076×10²³ entities.
Officially defined in 2019
candela
Measures luminous intensity
A typical candle emits luminous intensity near one candela.
Officially defined in 1979
SI Prefix Table
Prefixes let one unit scale from microscopic to planetary distances using powers of ten.
| Prefix | Symbol | Factor | Example |
|---|---|---|---|
| nano | n | 10?? | Modern chip features are measured in nanometers. |
| micro | µ | 10?6 | A human red blood cell is about 7 to 8 micrometers wide. |
| milli | m | 10?³ | A raindrop volume is often a few milliliters. |
| centi | c | 10?² | Most rulers use centimeter markings. |
| kilo | k | 10³ | A 5K race is 5 kilometers. |
| mega | M | 106 | City populations are often expressed in megascale counts. |
| giga | G | 10? | Internet speeds are sold in gigabits per second. |
| tera | T | 10¹² | Hard drives are commonly sized in terabytes. |