Temperature Converter

Temperature Conversion Formulas

All temperature conversions are based on the relationship between the scales' zero points and degree sizes.

The Celsius and Fahrenheit scales intersect at exactly −40° (−40°C = −40°F). This makes −40 a useful sanity-check number. The Kelvin scale uses the same degree size as Celsius but starts at absolute zero. Rankine uses the same degree size as Fahrenheit but also starts at absolute zero.

Mental Math Shortcuts for Temperature Conversion

You don't always need exact math — here are quick estimation tricks that work well for everyday temperatures.

°C → °F (quick): Double it and add 30. Example: 20°C → 20×2+30 = 70°F (actual: 68°F). Works best between 0-30°C, drift increases at extremes.

°F → °C (quick): Subtract 30 and halve it. Example: 80°F → (80−30)/2 = 25°C (actual: 26.7°C).

More accurate °C → °F: Double, subtract 10% of the doubled value, add 32. Example: 25°C → 50 − 5 + 32 = 77°F (exact!).

Anchor points to memorize: 0°C=32°F, 10°C=50°F, 20°C=68°F, 30°C=86°F, 37°C=98.6°F, 100°C=212°F. Interpolate between these for quick estimates.

Common Temperature Conversions

Here are the most frequently searched temperature conversions:

History of Temperature Scales

The Fahrenheit scale (1724) was the first standardized temperature scale, followed by Celsius (1742) and Kelvin (1848).

Fahrenheit was created by Daniel Gabriel Fahrenheit, a German physicist. He set 0°F as the temperature of a brine solution (the coldest he could reliably create), 32°F as the freezing point of water, and 96°F as body temperature (later corrected to 98.6°F). Only the US, Liberia, and the Cayman Islands still use Fahrenheit as their primary scale.

Celsius was proposed by Swedish astronomer Anders Celsius. Originally, his scale was inverted (0° = boiling, 100° = freezing) and was flipped by Carl Linnaeus after Celsius's death. It's used by virtually every country except the US.

Kelvin was proposed by Lord Kelvin (William Thomson) and is the SI base unit for temperature. It's essential in science because it starts at absolute zero, making it proportional to actual thermal energy. A temperature of 0 K means zero thermal energy — no colder temperature is physically possible.

Why Does the US Use Fahrenheit?

Historical inertia. The US adopted Fahrenheit in the colonial era from Britain, and unlike most countries, never switched when the metric system was adopted globally in the 1960s-70s.

The Metric Conversion Act of 1975 was voluntary, not mandatory, so adoption stalled. Proponents of Fahrenheit argue it has finer granularity for weather (the 0-100°F range roughly corresponds to the human comfort range, while in Celsius that's 0-37°), making it more intuitive for everyday use. Critics point out that Celsius's 0 = freezing and 100 = boiling anchors are more logical. In practice, Americans who work in science, medicine, or international business routinely use Celsius.

Cooking Temperature Conversions

Most recipes from Europe use Celsius; American recipes use Fahrenheit. Here are the essential cooking conversions:

Fan/convection ovens run about 20°C (35°F) hotter than conventional ovens at the same setting. When following a recipe for a conventional oven in a fan oven, reduce the temperature by 20°C or check 5-10 minutes earlier.

When Does Cold Become Dangerous? Temperature and Human Health

The human body maintains a core temperature of ~37°C (98.6°F). Deviations of just 2-3°C in either direction can be life-threatening.

Hypothermia stages: Mild (35-32°C / 95-90°F): shivering, confusion, poor coordination. Moderate (32-28°C / 90-82°F): shivering stops (bad sign), drowsiness, slurred speech. Severe (below 28°C / 82°F): loss of consciousness, cardiac arrest risk. Frostbite begins when skin temperature drops below -0.55°C (31°F), typically at air temperatures of -27°C (-17°F) or below with wind chill.

Heat dangers: Heat exhaustion occurs at body temps of 38-40°C (100-104°F): heavy sweating, weakness, nausea. Heat stroke above 40°C (104°F) is a medical emergency: confusion, hot dry skin, seizures. Ambient temperatures above 35°C (95°F) with high humidity become dangerous because sweat can no longer evaporate effectively. The "wet-bulb temperature" limit for human survival is approximately 35°C — above this, the body cannot cool itself regardless of shade, water, or fitness level.