Temperature Unit Converter

Convert temperatures between Kelvin, Celsius, and Fahrenheit. Essential for chemistry calculations that require absolute temperature.

Stoichiometry

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Reference points

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How to Use

  1. 1
    Enter the temperature value

    Type the numeric temperature value you want to convert into the input field for Kelvin, Celsius, or Fahrenheit.

  2. 2
    Select the source scale

    Choose Kelvin (K), Celsius (°C), or Fahrenheit (°F) as your starting scale. The tool applies the exact IUPAC conversion formulas.

  3. 3
    Read all three converted values

    Instantly see the equivalent temperature on all three scales simultaneously. Use the absolute zero reference (0 K = -273.15°C = -459.67°F) to check your results.

About

Temperature is one of the seven SI base quantities and is measured on three primary scales used in science and daily life. While the Celsius and Fahrenheit scales were developed empirically around the physical properties of water and human experience respectively, the Kelvin scale is thermodynamically fundamental: its zero point (absolute zero, 0 K) is defined by the absence of thermal energy, and its degree size is identical to the Celsius degree.

For chemists, the Kelvin scale is indispensable because temperature enters thermodynamic equations as an absolute quantity. The ideal gas law (PV = nRT), the Arrhenius equation for reaction rates (k = A·e^(-Ea/RT)), the Boltzmann distribution, and the Gibbs-Helmholtz equation all require temperature in Kelvin. Using Celsius in these formulas would introduce systematic errors that grow larger as temperature approaches 0°C.

Beyond thermodynamics, temperature calibration matters for spectroscopy, where peak positions and linewidths are temperature-dependent; for materials characterization, where phase diagrams specify transformation temperatures in °C; and for industrial process control, where setpoints may be specified in °F, °C, or K depending on the engineering tradition of the industry. This converter handles all three scales with exact IUPAC-compliant formulas, eliminating the rounding errors that accumulate in step-by-step manual conversions.

FAQ

What is the difference between Celsius, Fahrenheit, and Kelvin?
The Celsius scale (°C) sets 0° at the freezing point and 100° at the boiling point of water at standard pressure, and is used globally in science and everyday life outside the United States. The Fahrenheit scale (°F) uses 32° for freezing and 212° for boiling water, and remains in everyday use in the United States. The Kelvin scale (K) is the SI unit of thermodynamic temperature, with 0 K at absolute zero and the same degree size as Celsius, so T(K) = T(°C) + 273.15.
What is absolute zero and can it be reached?
Absolute zero (0 K = -273.15°C) is the lowest theoretically possible temperature, where all classical thermal motion ceases and a system is in its quantum mechanical ground state. The third law of thermodynamics (Nernst's heat theorem) states that absolute zero cannot be reached in a finite number of steps. Experimentally, ultracold atomic physics experiments have achieved temperatures within billionths of a Kelvin of absolute zero using laser cooling and magnetic trapping, but zero itself remains unreachable.
Why does chemistry use Kelvin rather than Celsius?
Most thermodynamic equations require an absolute temperature scale where zero genuinely means zero thermal energy. Using Celsius in the ideal gas law or Boltzmann's equation would give physically meaningless results: 0°C is not zero temperature, so gas volume or reaction rate at 0°C is not zero. The Kelvin scale avoids this problem. Standard thermodynamic tables report ΔH°, ΔG°, and K values at T = 298.15 K (25°C), but all calculations involving T must use Kelvin.
How do I convert Fahrenheit to Celsius?
The exact formula is T(°C) = (T(°F) - 32) × 5/9. A useful mental shortcut: subtract 32, then halve the result and add 10% of it (approximating ×5/9 ≈ ×0.556). For example, 98.6°F: subtract 32 = 66.6, halve = 33.3, add 10% of 33.3 ≈ 3.3, total ≈ 36.6°C (exact is 37.0°C). The reverse is T(°F) = T(°C) × 9/5 + 32.
At what temperature are Celsius and Fahrenheit equal?
The two scales intersect at -40° (-40°C = -40°F), which can be derived algebraically by setting T(°C) = T(°F) in the conversion formula. This coincidence is sometimes useful as a sanity check when doing manual conversions: if your converted Celsius and Fahrenheit values are both near -40 and equal, your arithmetic is consistent with this known fixed point.
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