Temperature Converter
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By Prof. David KimReviewed by Dr. Emily Watson, PhD (Thermodynamics)Published: Updated:
References
- [1]Bureau International des Poids et Mesures (BIPM), The International System of Units (SI) – 9th Edition, 2019. https://www.bipm.org/en/publications/si-brochure
- [2]National Institute of Standards and Technology (NIST), Guide for the Use of the International System of Units (SI), 2008. https://physics.nist.gov/cuu/pdf/sp811.pdf
- [3]International Organization for Standardization, ISO 80000-5: Quantities and Units – Part 5: Thermodynamics, 2019.
How to Use?
- 1
Enter the temperature value
Type the numeric temperature into the Value field. Use the unit dropdown to select Celsius (°C), Fahrenheit (°F), or Kelvin (K).
- 2
Select the source unit
Choose the unit of your input from the dropdown next to the value field. The calculator normalises all inputs to Celsius internally, so any unit works as the source.
- 3
Review all three equivalent values
The results panel displays the equivalent temperature in Celsius, Fahrenheit, and Kelvin simultaneously. All three are always shown regardless of which unit you entered.
- 4
Check decimal precision
Results are displayed with two decimal places, sufficient for weather, cooking, medical, and most laboratory applications.
- 5
Verify against known reference points
Cross-check results against common values: water freezes at 0 °C / 32 °F / 273.15 K, body temperature is 37 °C / 98.6 °F / 310.15 K.
- 6
Use related converters
For thermal energy and heat transfer calculations, use the <a href="/calculator/energy-converter">Energy Converter</a> on this site.
Worked Examples
1Convert 25 °C to Fahrenheit
Given Values
Temperature:25
tempValue_unit:C
Results
celsius:25
fahrenheit:77
kelvin:298.15
2Convert 98.6 °F to Celsius and Kelvin
Given Values
Temperature:37
tempValue_unit:C
Results
celsius:37
fahrenheit:98.6
kelvin:310.15
3Convert absolute zero from Kelvin
Given Values
Temperature:-273.15
tempValue_unit:C
Results
celsius:-273.15
fahrenheit:-459.67
kelvin:0
4Convert −40 °C to Fahrenheit
Given Values
Temperature:-40
tempValue_unit:C
Results
celsius:-40
fahrenheit:-40
kelvin:233.15
5Convert 350 °F (common oven temperature) to Celsius
Given Values
Temperature:176.67
tempValue_unit:C
Results
celsius:176.67
fahrenheit:350
kelvin:449.82
6Convert 300 K to Celsius and Fahrenheit
Given Values
Temperature:26.85
tempValue_unit:C
Results
celsius:26.85
fahrenheit:80.33
kelvin:300
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Frequently Asked Questions
Subtract 32 from the Fahrenheit value, then multiply by 5/9. For 98.6 °F: (98.6 − 32) = 66.6, times 5/9 = 37.0 °C. This formula works for any Fahrenheit temperature. A quick mental shortcut is to subtract 32, halve the result, then add about 10%. Use this converter for exact results without mental arithmetic.
Absolute zero is 0 K, −273.15 °C, or −459.67 °F. It is the lowest possible temperature where all molecular motion ceases at the classical level, leaving only quantum mechanical zero-point energy. Absolute zero is the starting point of the Kelvin scale and the foundation of the third law of thermodynamics. No physical system can reach exactly absolute zero through any finite process.
The two scales intersect at −40°, where −40 °C = −40 °F. This is the only temperature where the numeric value is the same in both scales. It is a useful reference point for quick mental conversion checks and a common trivia question in science education. Enter −40 in either unit in this converter to verify.
Kelvin is an absolute thermodynamic temperature scale, not a relative one. The degree symbol was officially removed by the 13th General Conference on Weights and Measures (CGPM) in 1967 because Kelvin is a unit of absolute temperature, not a degree of temperature. Writing “100 °K” is technically incorrect; the correct notation is “100 K” with a space between the number and the unit symbol. Celsius and Fahrenheit retain the degree symbol because they are relative scales with arbitrary zero points.
At standard atmospheric pressure (sea level), water boils at 100 °C, 212 °F, and 373.15 K. The boiling point decreases with altitude: at 1,500 metres (5,000 ft), water boils at approximately 95 °C (203 °F, 368 K). This is why cooking times and temperatures must be adjusted at high elevations.
The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in 1724 and became established in the English-speaking world through British colonial influence. The US continued using Fahrenheit after most other countries adopted the metric system and Celsius in the 19th and 20th centuries. The US considered metrication in the 1970s but the conversion was voluntary and never fully implemented. Today, the US uses Fahrenheit for everyday weather and cooking, Celsius for most scientific work, and Kelvin for thermodynamic calculations, creating a practical trilingual temperature environment.
−40 degrees. At −40°, the Celsius and Fahrenheit scales give the identical numeric value. This occurs because the linear relationship °F = (°C × 9/5) + 32 equals °C when °C = −40. Solving for the intersection: °F = °C → °C = (°C × 9/5) + 32 → °C − (°C × 9/5) = 32 → −(4/5)°C = 32 → °C = −40. This is a useful fact for quick mental conversions when dealing with extreme cold temperatures.
Common oven temperature equivalents: 140 °C = 275 °F (very low), 160 °C = 325 °F (low), 180 °C = 350 °F (moderate), 200 °C = 400 °F (hot), 220 °C = 425 °F (very hot), 240 °C = 475 °F (maximum for most domestic ovens). Use this converter for exact conversions when following recipes from different countries. The conversion formula is °F = (°C × 9/5) + 32. For gas mark ovens (common in the UK), gas mark 4 equals 180 °C (350 °F).
Temperature measures the average kinetic energy of particles in a substance and indicates the direction of energy flow. Heat is thermal energy transferred between systems due to a temperature difference. A large object at a moderate temperature contains more thermal energy than a small object at a high temperature. For example, a swimming pool at 25 °C contains vastly more thermal energy than a hot cup of coffee at 80 °C. Temperature and heat are related through the specific heat capacity of the substance: Q = mcΔT, where Q is heat energy, m is mass, c is specific heat capacity, and ΔT is the temperature change. This converter handles temperature units only; for energy conversions, use the Energy Converter.
The required precision depends entirely on the application. Weather forecasts need only integer precision: 22 °C (72 °F) is sufficient for deciding how to dress. Cooking typically needs 5–10 degree Fahrenheit or 2–5 degree Celsius precision. Medical thermometers require 0.1 °C or 0.2 °F precision. Laboratory measurements may need 0.01 °C or better, especially near phase transitions. This converter displays two decimal places, which covers weather, cooking, medical, and most routine laboratory applications. For higher precision, the formulas are exact; the display is the limiting factor.
Comfortable room temperature is typically 20–22 °C (68–72 °F, 293–295 K). The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends 21–23 °C (70–74 °F) for occupied indoor spaces. Standard room temperature for scientific purposes is often defined as 20 °C (68 °F, 293.15 K) or 25 °C (77 °F, 298.15 K) depending on the field and standard.
The ideal gas law PV = nRT requires absolute temperature in Kelvin. Using Celsius or Fahrenheit directly produces incorrect results because the relationship between pressure, volume, and temperature is proportional only when measured from absolute zero. For example, doubling the temperature of a gas from 27 °C to 54 °C does not double the pressure at constant volume. Converting to Kelvin: 27 °C = 300.15 K and 54 °C = 327.15 K. The actual pressure ratio is 327.15 / 300.15 = 1.09, not 2. Always convert to Kelvin before using any thermodynamic equation that involves temperature as a variable.
Kelvin is the standard for all thermodynamic calculations, gas law applications, and any equation where temperature appears as an absolute variable. Celsius is used for reporting measured temperatures in most scientific publications and for everyday laboratory measurements. Fahrenheit is rarely used in research except in some fields within the United States, such as food science and certain areas of biomedical research. The International Temperature Scale of 1990 (ITS-90) defines practical temperature standards from 0.65 K to approximately 1,358 K and is the basis for all modern temperature calibration, expressed in both Celsius and Kelvin.
Yes. A 0.5 °C error in body temperature measurement can change a diagnosis: 37.5 °C (99.5 °F) is normal while 38.0 °C (100.4 °F) indicates fever. Vaccine cold chain monitoring requires knowing exact thresholds: 2 °C (35.6 °F) and 8 °C (46.4 °F) define the acceptable range. An incorrectly converted Fahrenheit reading of 47 °F (8.3 °C instead of the correct 46.4 °F) could falsely indicate a temperature excursion. Always use a reliable converter for clinical temperature conversions and double-check against known reference points.
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