SI Unit Converter
Convert between SI units and common units for all physical quantities — length, mass, time, force, energy, power, pressure.
About SI Units
The International System of Units (SI) is the modern form of the metric system and the world's most widely used system of measurement. It defines seven base units: metre (length), kilogram (mass), second (time), ampere (electric current), kelvin (thermodynamic temperature), mole (amount of substance), and candela (luminous intensity).
The 7 SI base units form the foundation. All other units are derived from these, defined by fixed numerical values of fundamental constants.
SI prefixes (kilo, mega, giga, milli, micro, nano) scale units by powers of 10, allowing expression of very large and very small quantities.
SI units are coherent — derived units are formed by multiplying or dividing base units with no additional conversion factors needed.
Frequently asked questions
What is the SI base unit of length?
The metre (m) is the SI base unit of length. It is defined as the distance light travels in 1/299,792,458 of a second in vacuum.
How do I convert Celsius to Fahrenheit?
Use the formula: °F = (°C × 9/5) + 32. For example, 100°C = (100 × 9/5) + 32 = 212°F. To convert back: °C = (°F − 32) × 5/9.
What is the difference between mass and weight?
Mass is the amount of matter in an object (measured in kg), while weight is the force gravity exerts on that mass (measured in Newtons). Weight = mass × gravitational acceleration (9.8 m/s² on Earth).
How many joules are in a kilowatt-hour?
One kilowatt-hour (kWh) equals 3,600,000 joules (3.6 MJ). This is because 1 kW = 1000 W = 1000 J/s, and 1 hour = 3600 seconds, so 1 kWh = 1000 × 3600 = 3,600,000 J.
What is atmospheric pressure in Pascals?
Standard atmospheric pressure is 101,325 Pascals (101.325 kPa), also written as 1 atm or 760 mmHg or 14.696 psi. This is the average air pressure at sea level.