Temperature Converter
Convert temperatures across Celsius, Fahrenheit, and Kelvin.
How to use this temperature converter
- Enter the temperature
Type the number you want to convert into the Temperature value field.
- Choose the source scale
Select Celsius, Fahrenheit, or Kelvin from the From unit dropdown.
- Choose the target scale
Select the desired output scale from the To unit dropdown.
- Read the converted result
The Converted value appears instantly along with the Conversion path used.
How this temperature converter works
This temperature converter translates values among the three most widely used temperature scales — Celsius, Fahrenheit, and Kelvin — using the exact linear conversion formulas that have been standard in physics and engineering since the scales were formally defined. Celsius and Fahrenheit are related through a linear equation that accounts for their different zero points and degree sizes, while Kelvin is simply an offset of Celsius anchored at absolute zero (−273.15 °C). Because these conversions are exact linear transformations (not approximations), the results match reference tables published by NIST and other metrology bodies to full floating-point precision.
°F = °C × 9/5 + 32
°C = (°F − 32) × 5/9
K = °C + 273.15
°C = K − 273.15
°F = (K − 273.15) × 9/5 + 32
K = (°F − 32) × 5/9 + 273.15 Convert 72 °F to Celsius: °C = (72 − 32) × 5/9 = 40 × 5/9 = 22.22 °C. Convert 100 °C to Fahrenheit: °F = 100 × 9/5 + 32 = 180 + 32 = 212 °F. Convert 22.22 °C to Kelvin: K = 22.22 + 273.15 = 295.37 K. These results match the well-known reference points: water boils at 100 °C / 212 °F, and typical room temperature (72 °F) is about 22 °C or 295 K.
Body temperature averages about 37 °C. To express it in Fahrenheit: 37 × 9/5 + 32 = 98.6 °F. In Kelvin: 37 + 273.15 = 310.15 K.
An oven set to 350 °F converts to Celsius as (350 − 32) × 5/9 = 176.67 °C. Set the From unit to Fahrenheit and the To unit to Celsius for a quick check.
- ✓ All three conversions are exact linear transformations — no rounding or approximation is applied to the formulas themselves.
- ✓ Kelvin values below 0 are physically impossible (absolute zero is 0 K = −273.15 °C); the calculator will still compute them but they have no physical meaning.
- ✓ The Celsius scale used here is the modern definition tied to the kelvin via the 2019 SI redefinition, where one degree Celsius equals exactly one kelvin.
- ✓ Results are displayed rounded to two decimal places; internal arithmetic uses full floating-point precision.
- The formula °F = °C × 9/5 + 32 is exact by definition — memorizing it and the inverse covers the vast majority of everyday temperature conversions.
- At −40°, Celsius and Fahrenheit intersect: −40 °C = −40 °F. This is a useful mental anchor for checking your conversions.
- Kelvin is the SI base unit for thermodynamic temperature and is used in scientific contexts where ratios matter (e.g. gas laws, blackbody radiation). It has no degree symbol.
- For cooking and weather, Celsius-to-Fahrenheit is the most common conversion; for physics and chemistry, Celsius-to-Kelvin dominates.
- National Institute of Standards and Technology (NIST) — Guide for the Use of the International System of Units
- Bureau International des Poids et Mesures (BIPM) — The International System of Units (SI), 9th edition, 2019
Why three temperature scales exist
Fahrenheit was one of the first standardized temperature scales, developed in 1724 by Daniel Gabriel Fahrenheit. It set convenient reference points for early laboratory work but divided the range between those points into an unusual number of degrees. Celsius, introduced in 1742, simplified things by anchoring 0° and 100° at the freezing and boiling points of water at standard atmospheric pressure. Kelvin, adopted as the SI base unit for temperature in 1954, shifts the Celsius scale so that zero represents absolute zero — the lowest theoretically possible temperature. Each scale persists because it serves different communities: Fahrenheit is common in the United States for weather and cooking, Celsius is the default in most of the world, and Kelvin is essential in scientific and engineering contexts where negative values would break ratio-based formulas.
Common conversion pitfalls
The most frequent mistake when converting temperatures is forgetting that the formulas involve both a scaling factor and an offset. Multiplying a Celsius value by 9/5 without adding 32 yields a wrong result. Another common pitfall is confusing temperature differences with absolute temperatures: a change of 10 °C equals a change of 18 °F, but 10 °C as a reading is 50 °F, not 18 °F. When working with Kelvin, remember that there is no degree symbol — write 300 K, not 300 °K. Finally, negative Kelvin values are physically meaningless; if your calculation returns one, double-check the input.
Temperature converter FAQs
Why do Celsius and Fahrenheit use different zero points?
Celsius sets 0° at the freezing point of water and 100° at its boiling point (at standard atmospheric pressure). Fahrenheit originally set 0° at the coldest temperature Daniel Fahrenheit could produce with a salt-ice mixture and 96° at approximate human body temperature. The two scales were designed independently with different reference points.
Is there a quick mental trick for Celsius to Fahrenheit?
A common approximation is to double the Celsius value and add 30. For example, 20 °C ≈ 2 × 20 + 30 = 70 °F (the exact answer is 68 °F). It works reasonably well for everyday temperatures between 0 °C and 40 °C.
What is absolute zero and why does it matter?
Absolute zero (0 K, −273.15 °C, −459.67 °F) is the theoretical lowest temperature where all classical thermal motion ceases. It serves as the anchor for the Kelvin scale and is critical in thermodynamics, cryogenics, and quantum physics.
When should I use Kelvin instead of Celsius?
Use Kelvin whenever a formula involves temperature ratios or proportionalities — for example, the ideal gas law (PV = nRT), Stefan-Boltzmann radiation, or Carnot efficiency. Kelvin avoids negative values that would break ratio-based calculations.
Does this converter handle Rankine or other scales?
This tool covers Celsius, Fahrenheit, and Kelvin, which are the three scales used in virtually all modern science, engineering, cooking, and weather contexts. Rankine (°R = °F + 459.67) is rarely needed outside specialized U.S. engineering applications.