What is the SI unit for temperature?

• A. Kelvin
• B. Celsius
• C. Fahrenheit
• D. Newton

Answer: (A)

Kelvin is the SI unit used for measuring temperature in science. It’s the SI base unit for thermodynamic temperature, with 0 K representing absolute zero—the theoretical lowest possible temperature where particles have minimal motion. The size of one kelvin is the same as one degree Celsius, so temperatures in kelvin are related to Celsius by adding 273.15 (K = C + 273.15). This makes kelvin especially convenient in scientific calculations, such as the ideal gas law, where using kelvin avoids negative temperatures and keeps equations consistent. Celsius is a widely used temperature scale but not an SI base unit, Fahrenheit is another scale used in some places, and Newton is a unit of force, not temperature.