Temperature Converter
Convert between Celsius, Fahrenheit, and Kelvin temperature units. Perfect for cooking, science, and everyday use.
Common Temperatures
Everyday Calculators
Understanding Temperature Scales
The Three Main Temperature Scales
Temperature is a measure of thermal energy and how hot or cold an object is. Though we experience temperature directly, measuring it precisely requires standardized scales. The three main temperature scales used around the world are Celsius, Fahrenheit, and Kelvin, each with its own history, reference points, and applications.
Celsius (°C)
Key Reference Points
- 0°C = Water freezing point
- 100°C = Water boiling point
- (at standard atmospheric pressure)
Developed by: Anders Celsius (1742)
Originally called: Centigrade scale
Primary usage: Most countries worldwide for daily life, science, and meteorology
Advantages: Decimal-based with intuitive reference points tied to water
Fahrenheit (°F)
Key Reference Points
- 32°F = Water freezing point
- 212°F = Water boiling point
- 98.6°F = Average human body temperature
Developed by: Daniel Gabriel Fahrenheit (1724)
Original reference: Based on brine solution freezing point (0°F) and human body temperature (96°F)
Primary usage: United States and its territories for daily life and non-scientific applications
Advantages: Finer granularity for weather reporting without using decimals
Kelvin (K)
Key Reference Points
- 0K = Absolute zero (-273.15°C)
- 273.15K = Water freezing point
- 373.15K = Water boiling point
Developed by: Lord Kelvin (William Thomson) (1848)
Special attribute: Begins at absolute zero, the lowest theoretically possible temperature
Primary usage: Scientific research, thermodynamics, physics, chemistry
Note: Uses the same increment size as Celsius but no negative values
Temperature Conversion Formulas
Celsius to Fahrenheit
°F = (°C × 9/5) + 32
Example: Convert 25°C to Fahrenheit
°F = (25 × 9/5) + 32 = 45 + 32 = 77°F
Fahrenheit to Celsius
°C = (°F - 32) × 5/9
Example: Convert 98.6°F to Celsius
°C = (98.6 - 32) × 5/9 = 66.6 × 5/9 = 37°C
Celsius/Fahrenheit to Kelvin
K = °C + 273.15
K = (°F - 32) × 5/9 + 273.15
Example: Convert 0°C to Kelvin
K = 0 + 273.15 = 273.15K
Key Reference Points Across Scales
| Physical Phenomenon | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) |
|---|---|---|---|
| Absolute Zero | -273.15 | -459.67 | 0 |
| Water Freezing | 0 | 32 | 273.15 |
| Room Temperature | 20-22 | 68-72 | 293-295 |
| Human Body Temperature | 37 | 98.6 | 310.15 |
| Water Boiling | 100 | 212 | 373.15 |
| Oven Baking | 175-200 | 350-400 | 448-473 |
Historical Context
Development of Temperature Measurement
- Early 1600s: Galileo Galilei creates one of the first thermoscopes, a device that showed temperature changes but without standardized measurements.
- 1724: Daniel Fahrenheit creates the mercury thermometer and the Fahrenheit scale. He set 0°F as the temperature of a mixture of ice, water, and ammonium chloride, and 96°F as approximate human body temperature.
- 1742: Anders Celsius proposes a scale where 0° was water's boiling point and 100° was water's freezing point. This was later reversed to the current system.
- 1848: Lord Kelvin proposes an absolute temperature scale starting at absolute zero, the theoretical point where molecular motion stops.
Modern Adoption Patterns
The global adoption of temperature scales follows historical and cultural patterns:
Celsius Dominance
Most countries worldwide use Celsius for everyday temperature measurement, weather reporting, and cooking. This standardization occurred with the metric system adoption, particularly accelerating during the 20th century.
Fahrenheit Persistence
The United States remains the primary user of Fahrenheit for daily life, along with a few territories like Puerto Rico. Some older generations in countries that formally switched to Celsius (like the UK and Canada) still use Fahrenheit informally.
Kelvin in Science
Kelvin is universally used in scientific contexts worldwide, regardless of which scale is used in daily life. It's the SI unit for temperature and is essential in thermodynamics, physics, chemistry, and astronomy.
Practical Applications
Cooking & Baking
Understanding temperature conversions is crucial for following international recipes. US recipes use °F for oven temperatures, while most other countries use °C. Precision is especially important in baking, where exact temperatures affect chemical reactions in the food.
Weather & Travel
Travelers need to interpret weather forecasts in different units depending on location. A comfortable 75°F is about 24°C; a freezing 0°C is 32°F. Weather apps often allow switching between units, but understanding conversions helps with rapid mental approximations.
Science & Education
Scientific work requires familiarity with all scales but primarily uses Celsius and Kelvin. Kelvin is essential for understanding concepts like absolute zero and thermodynamic laws. Converting between scales is a common skill taught in physics and chemistry education.
Quick Conversion Tricks
Celsius to Fahrenheit (Approximate)
For a quick mental approximation:
- Double the Celsius temperature
- Subtract 10% of this value
- Add 32
Example: Convert 20°C to Fahrenheit
- Double: 20 × 2 = 40
- Subtract 10%: 40 - 4 = 36
- Add 32: 36 + 32 = 68°F
- (Actual: 68°F)
Fahrenheit to Celsius (Approximate)
For a quick mental approximation:
- Subtract 30 from the Fahrenheit temperature (not exactly 32, for easier mental math)
- Divide by 2
Example: Convert 86°F to Celsius
- Subtract 30: 86 - 30 = 56
- Divide by 2: 56 ÷ 2 = 28°C
- (Actual: 30°C)
Note: This is less accurate for extreme temperatures; for a more precise result, subtract 32 and multiply by 5/9.
Special Temperature Concepts
Absolute Zero
Absolute zero is the lowest theoretically possible temperature, where all molecular motion and thermal energy are minimized. It represents the fundamental lower limit of temperature in the universe.
- Defined as 0 Kelvin (-273.15°C or -459.67°F)
- Cannot be reached in practice due to quantum effects
- Scientists have achieved temperatures within billionths of a degree above absolute zero
- At absolute zero, a perfect crystal would have zero entropy
Temperature Extremes
Our universe spans an incredible range of temperatures:
- Coldest natural place: Boomerang Nebula at -272°C (1 Kelvin)
- Coldest laboratory temperature: Below 0.000000001 Kelvin using magnetic cooling
- Hottest natural place on Earth: Lut Desert, Iran reaching 80.8°C (177.4°F)
- Hottest laboratory temperature: Over 5.5 trillion degrees Celsius achieved in particle collisions
- Stellar cores: 15 million°C in our sun
- Supernova explosions: Can reach billions of degrees
Temperature and Climate Considerations
Temperature measurement plays a crucial role in understanding climate patterns and changes. Global temperature records typically use Celsius, with changes measured in fractions of degrees having significant implications for climate science.
When discussing global warming, scientists often refer to temperature anomalies—deviations from a baseline average rather than absolute temperatures. For example, a global temperature increase of 1.5°C above pre-industrial levels is a key threshold identified by climate scientists as having potentially significant impacts.
Understanding temperature scales helps citizens interpret climate data and participate in informed discussions about environmental policies and practices.
Lesser-Known Temperature Scales
While Celsius, Fahrenheit, and Kelvin are the most widely used temperature scales, several other scales have been developed for specific purposes or historical contexts:
Rankine Scale (°R)
Developed in 1859 by William John Macquorn Rankine, this scale uses the Fahrenheit degree size but starts at absolute zero (like Kelvin does for Celsius). 0°R = absolute zero, and water freezes at 491.67°R. Used in some engineering fields in the US.
Réaumur Scale (°Ré)
Created in 1730 by René Antoine Ferchault de Réaumur, this scale sets 0° as water's freezing point and 80° as water's boiling point. Widely used in Europe, especially France, during the 18th and 19th centuries before Celsius became standardized.
Delisle Scale (°D)
Created in 1732 by Joseph-Nicolas Delisle, this scale runs opposite to most others: 0° is water's boiling point, and 150° is water's freezing point. It was used primarily in Russia for almost a century before being replaced by Celsius.