Temperature Converter

How the Temperature Converter Works

Type any temperature in Celsius, Fahrenheit, Kelvin, or Rankine — the other three fields update instantly. The converter uses the standard formulas: °F = °C × 9/5 + 32, K = °C + 273.15, and °R = K × 9/5. Kelvin and Rankine are both absolute scales starting at 0 (absolute zero); Kelvin uses Celsius-sized degrees while Rankine uses Fahrenheit-sized degrees.

Click any preset in the scientific reference panel to load all four values at once.

Understanding Temperature Scales

The Fahrenheit scale was developed by German physicist Daniel Gabriel Fahrenheit in 1724, who invented the mercury thermometer and needed a consistent scale to calibrate it. Fahrenheit defined 32°F as the freezing point of water and 212°F as the boiling point, with human body temperature falling at approximately 98.6°F. His scale was widely adopted in the English-speaking world and remains the official standard in the United States today, primarily because of deep-rooted historical convention and the cost of switching infrastructure, education, and everyday references.

The Celsius scale — originally called centigrade — was proposed by Swedish astronomer Anders Celsius in 1742. Celsius anchored his scale to the behavior of water: 0°C for freezing, 100°C for boiling at sea level. This elegant, base-10 design made it the natural choice for science and most of the world. After World War II, the metric system (and Celsius with it) was adopted internationally, which is why nearly every country outside the United States uses Celsius for weather, cooking, and medicine. The name was officially changed from centigrade to Celsius in 1948 to honor its inventor.

The Kelvin scale was introduced by Irish-Scottish physicist William Thomson, later known as Lord Kelvin, in 1848. Unlike Celsius and Fahrenheit, Kelvin is an absolute scale — it starts at absolute zero (0 K), the theoretical minimum temperature where all molecular motion stops. There are no negative values on the Kelvin scale. Scientists and engineers use Kelvin in thermodynamics, astrophysics, and materials science because equations involving temperature ratios only work correctly when using an absolute scale. Here's the thing: doubling the Kelvin temperature truly means twice as much thermal energy — doubling Celsius doesn't. 0 K equals −273.15°C, or −459.67°F.

Quick Reference: Common Temperatures

• Water freezes — 0°C / 32°F / 273.15 K. The freezing point of pure water at standard atmospheric pressure (1 atm). This is the lower anchor point of the Celsius scale and one of the most universally recognized temperature references.
• Human body temperature — 37°C / 98.6°F / 310.15 K. Normal core body temperature in a healthy adult. In practice, body temperature varies throughout the day (slightly lower in the morning, higher in the evening) and between individuals, ranging from about 36.1°C to 37.2°C.
• Water boils — 100°C / 212°F / 373.15 K. The boiling point of pure water at sea level. At higher altitudes, lower atmospheric pressure causes water to boil at lower temperatures — on Mount Everest, water boils at approximately 70°C, which is why cooking times need adjustment at altitude.
• Room temperature — 20–22°C / 68–72°F / 293–295 K. The typical comfortable indoor temperature range for most humans. HVAC systems in offices and homes are commonly set to this range, and many scientific experiments specify "room temperature" as approximately 20°C (293 K).
• Absolute zero — −273.15°C / −459.67°F / 0 K. The lowest possible temperature in the universe, where all classical thermal motion ceases. It has never been perfectly achieved in a laboratory, though scientists have cooled matter to within a few billionths of a degree above it using techniques like laser cooling and magnetic evaporation.

Frequently Asked Questions