Temperature Converter

This converter translates a temperature value among Celsius (°C), Fahrenheit (°F), kelvin (K), Rankine (°R), and Réaumur (°Ré). It first converts the input to Celsius and then applies the selected output scale.

Temperature scales require both a scale factor and, for some pairs, an offset. They cannot all be handled by multiplying by one constant.

Formulas used

The calculator uses these relationships:

K = °C + 273.15
°C = K − 273.15
°F = °C × 9 ÷ 5 + 32
°C = (°F − 32) × 5 ÷ 9
°R = K × 9 ÷ 5
K = °R × 5 ÷ 9
°Ré = °C × 4 ÷ 5
°C = °Ré × 5 ÷ 4

The kelvin symbol is K, without a degree sign. The degree Celsius is equal in magnitude to the kelvin for temperature intervals, but the two scales have different zero points. Rankine is an absolute scale with Fahrenheit-sized intervals.

Worked example

To convert 68 °F to Celsius:

°C = (68 − 32) × 5 ÷ 9 = 20 °C

Then the same physical temperature in kelvin is:

K = 20 + 273.15 = 293.15 K

For a Rankine check, 491.67 °R converts to kelvin as:

K = 491.67 × 5 ÷ 9 = 273.15 K

and therefore to 0 °C. Small floating-point differences may be rounded in the displayed output.

What the result means

The result represents the same temperature expressed on another scale. It does not change the underlying physical state. An interval is different from an absolute temperature: for example, a change of 1 °C equals a change of 1 K, but 1 °C as a temperature is 274.15 K.

Common water reference points are conditional, not universal constants for every situation. At standard atmospheric pressure, water freezes near 0 °C and boils near 100 °C, but pressure, dissolved substances, purity, and the measurement standard affect phase-transition temperatures. Do not use a rounded conversion as a substitute for calibrated process measurements.

Scale and measurement limits

The converter rejects thermodynamic temperatures below absolute zero:

below −273.15 °C;
below −459.67 °F;
below 0 K;
below 0 °R;
below −218.52 °Ré.

Absolute zero itself is accepted. Values below absolute zero are rejected because they fall outside the ordinary thermodynamic temperature scales implemented here. The page does not model specialized negative-temperature states used in limited statistical-mechanics contexts.

Other limitations include:

Input uncertainty carries through the conversion. More displayed digits do not make an approximate measurement more accurate.
The browser uses floating-point arithmetic, so some decimal results are approximations before display rounding.
The converter handles temperature values, not sensor calibration, heat transfer, thermal expansion, cooking safety, fever assessment, or material limits.
Réaumur is included for historical and reference use; confirm the expected convention before using it with archival data.
For regulated, laboratory, industrial, or medical work, use calibrated instruments, appropriate uncertainty analysis, and the governing standard.

Sources

Editorial record

Written and manually reviewed by the SoupCalc Editorial Team. Every scale formula, absolute-zero boundary, symbol, and worked example was checked against the calculator implementation and official metrology references. Last reviewed: August 10, 2026. This page remains unavailable for indexing and advertising until all approved localizations pass review.