The three common temperature scales
Celsius (°C) is used in most of the world including India for everyday and scientific purposes. Fahrenheit (°F) is used mainly in the United States for everyday purposes. Kelvin (K) is the scientific base unit of temperature, used throughout physics and engineering because it starts at absolute zero rather than an arbitrary point.
How the conversions work
Celsius and Fahrenheit both use arbitrary reference points (0°C and 100°C are water’s freezing and boiling points at sea level; Fahrenheit uses different reference points), so converting between them requires both a scaling factor and an offset — not just multiplication. Kelvin uses the same size “degree” as Celsius, but shifts the zero point to absolute zero (–273.15°C), so converting between Celsius and Kelvin is a simple offset with no scaling needed.
Where mixing up scales causes real problems
- Cooking: oven temperatures and recipes from different countries are often written in different scales.
- Weather: comparing forecasts from sources that default to different scales.
- Science and engineering: many formulas require Kelvin specifically, not Celsius or Fahrenheit.
- Health: body temperature thresholds look very different numerically in Celsius vs Fahrenheit, which can cause confusion when reading a thermometer from an unfamiliar scale.
A quick sanity check
Room temperature is roughly 20–25°C, which is roughly 68–77°F, and roughly 293–298 K. If a conversion result is far outside a range that makes sense for the context, double-check which direction the conversion was done.