Convert a temperature reading or a change in temperature across five scales. The separate difference mode prevents offsets from being applied to a rise or fall.
Reading or change: choose the right mode
Use Temperature reading for a thermometer value such as 20°C. Use Temperature difference for a change such as warming by 20°C. These are different calculations: 20°C is 68°F, while an increase of 20°C is an increase of 36°F. The difference mode applies scale factors without adding the offsets used for absolute readings.
Choose source and destination scales and display precision. All-scale results use your entered value. The reference table offers examples on every supported scale; in difference mode each column is explicitly marked as a change.
Celsius, Fahrenheit and absolute scales
Celsius and kelvin have equal-sized intervals but different zero points. Fahrenheit and Rankine share their interval size, and Rankine starts at absolute zero. Réaumur has 80 degrees between the conventional freezing and boiling reference points of water, compared with 100 on Celsius.
An ordinary absolute temperature cannot fall below 0 K, equivalent to −273.15°C or −459.67°F. The reading mode rejects values below that limit. Difference mode allows negative values because they mean cooling, not a negative absolute temperature.
Measurement precision and practical limits
The formulas define unit relationships; they do not improve a thermometer's accuracy. Choose a suitable number of significant digits for the original measurement. The reference values are mathematical comparisons, not medical thresholds or cooking instructions. For appliance-method adjustments rather than a simple scale conversion, use the Air Fryer Converter.
NIST explains the temperature scales and exact conversion relationships.
Formula
°F = °C × 1.8 + 32
°C = (°F − 32) ÷ 1.8
K = °C + 273.15
°R = K × 1.8
°Ré = °C × 0.8
Temperature change: Δ°F = Δ°C × 1.8
Examples
The same reading on two scales
20°C × 1.8 + 32 = 68°F. On the kelvin scale this is 293.15 K.
A fall in temperature
A change of −10°C is −18°F or −10 K. Do not add 32 to a difference.
The common negative point
An absolute reading of −40°C equals −40°F.
Precision and definitions
Calculations retain unrounded values internally. Displayed digits do not increase the accuracy of measurements. NIST unit definitions provide the conversion reference.