Temperature quantifies the average kinetic energy of microscopic particles (atoms and molecules) within matter, determining the magnitude and direction of heat flow. Across weather forecasting, clinical medicine, aerospace engineering, HVAC refrigeration, cooking, and thermodynamics, temperature measurement relies on five major international scales: Celsius (°C), Fahrenheit (°F), Kelvin (K), Rankine (°R), and Réaumur (°r), anchored by physical constants such as Absolute Zero (0 K) and the Triple Point of Water (273.16 K).
Our free online Temperature Converter provides instant, high-precision conversions across all thermodynamic, metric, imperial, culinary, and historic temperature scales:
- Celsius to Fahrenheit:
°F = (°C × 1.8) + 32(Water freezes at 32 °F and boils at 212 °F). - Fahrenheit to Celsius:
°C = (°F - 32) ÷ 1.8(Water freezes at 0 °C and boils at 100 °C). - Celsius to Kelvin:
K = °C + 273.15(0 K = -273.15 °C = Absolute Zero). - Fahrenheit to Kelvin:
K = (°F - 32) ÷ 1.8 + 273.15(0 K = -459.67 °F). - Rankine to Kelvin:
K = °R ÷ 1.8(Rankine is the absolute thermodynamic scale for Fahrenheit: 0 °R = 0 K). - Réaumur to Celsius:
°C = °r × 1.25(0 °r = water freezing, 80 °r = water boiling). - Triple Point of Water:
1 Triple Point = 273.16 K = 0.01 °C = 32.018 °F(at 611.657 Pa pressure).
Master Temperature Conversion Table & Exact Formulas
The table below displays exact mathematical equations, conversion multipliers, and equivalent baseline values across all five major temperature scales relative to 0 °Celsius (273.15 K):
| Temperature Scale | Symbol | Conversion Formula to Celsius (°C) | Equivalent at Water Freezing (0 °C) | System & Application Field |
|---|---|---|---|---|
| Celsius (Centigrade) | °C |
°C = K - 273.15 |
0.0 °C |
Global Metric & Scientific Scale (SI Derived) |
| Fahrenheit | °F |
°F = (°C × 1.8) + 32 |
32.0 °F |
US Customary & Weather Forecasting Scale |
| Kelvin | K |
K = °C + 273.15 |
273.15 K |
SI Base Thermodynamic Scale (2019 Boltzmann Definition) |
| Rankine | °R, °Ra |
°R = (°C + 273.15) × 1.8 |
491.67 °R |
US Engineering Thermodynamic Absolute Scale |
| Réaumur | °r, °Re |
°r = °C × 0.8 |
0.0 °r |
Historical European & Cheese Manufacturing Scale |
| Triple Point of Water | TPW |
273.16 K = 0.01 °C |
1.000036 TPW (0.01 °C) | Thermodynamic Calibration Equilibrium Constant |
Step-by-Step Calculation Example
To convert an oven baking temperature of 200 °Celsius (200 °C) into Fahrenheit (°F) and Kelvin (K):
°F = (200 × 1.8) + 32 = 360 + 32 = 392 °Fahrenheits (392 °F)
K = 200 + 273.15 = 473.15 Kelvin (473.15 K)
Thus, a 200 °C oven temperature equals 392 °F (or 473.15 K).
Key Physical Temperature Scale Benchmarks
Below is a comparative reference chart showing temperature benchmarks across cryogenics, weather extremes, human body physiology, industrial metallurgy, and astrophysics:
| Physical State / Environment | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) | Rankine (°R) | Physical Context |
|---|---|---|---|---|---|
| Absolute Zero (Zero Molecular Motion) | -273.15 °C | -459.67 °F | 0.0 K | 0.0 °R | Lowest possible quantum thermodynamic state |
| Liquid Nitrogen Boiling Point (1 atm) | -195.79 °C | -320.42 °F | 77.36 K | 139.25 °R | Cryogenic industrial refrigerant fluid point |
| Scale Convergence Point (°C = °F) | -40.0 °C | -40.0 °F | 233.15 K | 419.67 °R | Exact mathematical equality point for °C and °F |
| Water Freezing / Ice Melting Point | 0.0 °C | 32.0 °F | 273.15 K | 491.67 °R | Standard atmospheric liquid-solid phase boundary |
| Triple Point of Water (TPW) | 0.01 °C | 32.018 °F | 273.16 K | 491.688 °R | Coexistence of ice, water, and vapor (611.657 Pa) |
| Standard Room Temperature | 20.0 °C | 68.0 °F | 293.15 K | 527.67 °R | NIST indoor ambient laboratory temperature |
| Normal Human Body Temperature | 37.0 °C | 98.6 °F | 310.15 K | 558.27 °R | Physiological homeostatic core body mean |
| Water Boiling Point (1 atm) | 100.0 °C | 212.0 °F | 373.15 K | 671.67 °R | Standard sea-level liquid-gas phase transition |
| Sun Photosphere Surface Temperature | 5,504.85 °C | 9,940.73 °F | 5,778.0 K | 10,400.4 °R | Blackbody solar surface effective radiation temperature |
History & Standards: Fahrenheit vs. Celsius vs. Lord Kelvin’s Absolute Scale
Daniel Gabriel Fahrenheit (1724)
German physicist and glassblower Daniel Gabriel Fahrenheit (1686–1736) invented the precision mercury thermometer in 1714. In 1724, he established the Fahrenheit scale (°F) using three baseline reference points: 0 °F (freezing of an ice, water, and ammonium chloride brine mixture), 32 °F (ice melting in water), and 96 °F (healthy human body temperature). The scale was later calibrated so water boils at exactly 212 °F.
Anders Celsius and Carl Linnaeus (1742 / 1745)
Swedish astronomer Anders Celsius (1701–1744) proposed a centigrade scale in 1742. Interestingly, Celsius originally set 0 °C as the boiling point of water and 100 °C as the freezing point! Following Celsius’s death in 1744, famous botanist Carl Linnaeus inverted the scale in 1745 into the modern format: 0 °C for freezing water and 100 °C for boiling water.
Lord Kelvin and the 2019 Boltzmann Redefinition (1848 / 2019)
In 1848, Scottish physicist William Thomson (Lord Kelvin) calculated that molecular motion completely ceases at -273.15 °C, creating the absolute thermodynamic scale. In 1954, the 10th CGPM adopted the Kelvin (K) as the SI unit of temperature. On May 20, 2019, the 26th CGPM redefined the Kelvin using the exact fixed numerical value of the Boltzmann constant (k = 1.380649 × 10-23 J/K).
Popular direct conversions:
- Celsius to Fahrenheit Converter | Fahrenheit to Celsius Converter
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Frequently Asked Questions (FAQ)
What is the formula to convert Celsius (°C) to Fahrenheit (°F)?
To convert Celsius to Fahrenheit, multiply by 1.8 and add 32: °F = (°C × 1.8) + 32 (e.g., 25 °C × 1.8 + 32 = 77 °F).
What is the formula to convert Fahrenheit (°F) to Celsius (°C)?
To convert Fahrenheit to Celsius, subtract 32 and divide by 1.8: °C = (°F - 32) ÷ 1.8 (e.g., (98.6 °F – 32) ÷ 1.8 = 37 °C).
At what temperature are Celsius and Fahrenheit equal?
Celsius and Fahrenheit are equal at exactly -40 degrees (-40 °C = -40 °F).
What is Absolute Zero?
Absolute Zero is the lowest theoretical temperature where all classical atomic thermal motion stops, defined as 0 Kelvin (0 K), -273.15 °Celsius, or -459.67 °Fahrenheit.
What is the Triple Point of Water?
The Triple Point of Water is the unique thermodynamic condition where solid ice, liquid water, and water vapor coexist in stable equilibrium at exactly 273.16 Kelvin (0.01 °C / 32.018 °F) under a partial vapor pressure of 611.657 Pascals.