Temperature Calculator

Convert between Celsius, Fahrenheit, Kelvin, and other temperature scales. Calculate heat-related measurements and analyze thermal properties.

About Temperature Calculator

The Evolution of Temperature Measurement

The history of temperature measurement is a fascinating journey through human innovation. Early attempts relied on subjective feelings of hot and cold until the 16th century when Galileo Galilei created the first thermoscope. The modern era of thermometry began with Gabriel Fahrenheit's mercury thermometer in the early 1700s, followed by Anders Celsius's centigrade scale in 1742. The Kelvin scale, introduced by William Thomson in 1848, revolutionized temperature measurement by establishing an absolute zero point.

Temperature Conversion Formulas

Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Fahrenheit to Celsius: °C = (°F - 32) × 5/9
Celsius to Kelvin: K = °C + 273.15
Kelvin to Celsius: °C = K - 273.15
Rankine: °R = (°C + 273.15) × 9/5
Réaumur: °Ré = °C × 0.8
Rømer: °Rø = (°C × 21/40) + 7.5

Temperature Scales Compared

Scale	Water Freezing	Water Boiling	Common Use
Celsius (°C)	0°C	100°C	Most countries
Fahrenheit (°F)	32°F	212°F	USA, territories
Kelvin (K)	273.15K	373.15K	Scientific use

Historical Temperature Scales

Lesser-Known Scales

Réaumur scale (1730s): Used in Europe for alcohol content
Rankine scale (1859): Absolute scale based on Fahrenheit
Rømer scale (1701): First standardized thermometer
Newton scale: Based on linseed oil expansion

Historical Applications

Wine making and brewing
Early industrial processes
Medical diagnostics
Weather observation

Modern Temperature Measurement

Digital Technologies

Infrared thermometers
Fiber optic sensors
Thermal imaging cameras
Semiconductor sensors

Advanced Applications

Medical diagnostics
Industrial process control
Climate monitoring
Scientific research

Learn More

NIST Temperature Units ITS-90 Standard

Frequently Asked Questions

Why are there so many different temperature scales?

Different temperature scales were developed for different purposes and in different historical contexts. Celsius (°C) was designed around the freezing and boiling points of water (0°C and 100°C). Fahrenheit (°F) was based on a mixture of ice, water, and ammonium chloride (0°F) and average human body temperature (96°F, later adjusted). Kelvin (K) is an absolute scale starting at absolute zero (-273.15°C), making it useful for scientific calculations. Other scales like Rankine, Réaumur, and Rømer were developed for specific scientific or regional needs.

What's the difference between absolute and relative temperature scales?

Absolute temperature scales (like Kelvin and Rankine) start at absolute zero, the theoretical lowest possible temperature where all molecular motion stops. These scales don't have negative values. Relative scales (like Celsius and Fahrenheit) are based on observable phenomena like water's freezing and boiling points, and can have negative values. Absolute scales are essential in scientific calculations because many physical laws work only with absolute temperatures. For example, the ideal gas law requires temperature in Kelvin.

Why use these temperature units in different situations?

Different temperature scales are preferred in different contexts: Celsius is used in most countries for daily life and scientific work; Fahrenheit is common in the US for weather and body temperature; Kelvin is standard in scientific calculations and international standards; Rankine is used in some engineering applications in the US. In scientific work, it's often necessary to convert between scales - for example, a chemical reaction might be measured in Celsius but calculations might need Kelvin for thermodynamic equations.