Temperature Converter Online — Celsius, Fahrenheit & Kelvin Free

Temperature Conversion Formulas

How to Use the Temperature Converter

1. Enter the temperature value. Type the number you want to convert into the input field. Decimals are supported.
2. Select the source scale. Choose Celsius, Fahrenheit, or Kelvin from the dropdown or by clicking the scale label.
3. Read the conversions. All equivalent values in the other scales appear instantly. No submit button required — the result updates as you type.

Common Temperature Reference Points

Which Scale Is Used Where?

Celsius (°C)

Celsius is the standard temperature scale in everyday use across most of the world. Water freezes at 0°C and boils at 100°C at sea level — a memorable scale that makes intuitive sense for weather and cooking. The SI system uses Celsius for everyday temperatures and Kelvin for scientific work.

Fahrenheit (°F)

Fahrenheit is primarily used in the United States and a few other countries. It was defined with human body temperature as a reference (originally 98 °F, later standardised to 98.6 °F) and water freezing at 32 °F. For weather, US residents think in Fahrenheit — 32 °F is cold, 72 °F is comfortable, 100 °F is dangerously hot.

Kelvin (K)

Kelvin is the SI base unit for thermodynamic temperature, used in physics, chemistry, and engineering. Unlike Celsius and Fahrenheit, Kelvin has no negative values — it starts at absolute zero (the coldest possible temperature, where all thermal motion stops). Note that Kelvin temperatures are written without a degree symbol: "300 K" not "300 °K."

Quick Mental Conversion Tricks

For a rough Celsius to Fahrenheit conversion in your head: double the Celsius value and add 30. For example, 20°C → 40 + 30 = 70°F (actual: 68°F — close enough for weather). For Fahrenheit to Celsius: subtract 30 and halve. For example, 70°F → 40 ÷ 2 = 20°C.

The scales are equal at −40° (−40°C = −40°F), which is a useful memory anchor for extreme cold comparisons.

Common Questions

Why does the US still use Fahrenheit?

The US officially adopted the metric system through legislation in 1975 but never mandated it for everyday use. Fahrenheit became deeply embedded in everyday life through weather reports, thermostats, and cooking — switching requires changing cultural habits, not just legislation. Scientific, medical, and pharmaceutical industries in the US use Celsius and metric units; the consumer sector largely does not.

Is there a temperature below absolute zero?

In classical thermodynamics, no — absolute zero (0 K) is the theoretical lower limit. However, in quantum systems, physicists have created states described as having "negative temperature" in a statistical mechanics sense — these are actually hotter than any positive temperature, not colder, because of how the population of energy states is inverted. These are not temperatures below absolute zero in the everyday sense.