Temperature converter guide
Temperature-scale conversion is affine: Celsius and Fahrenheit have different zero points as well as different degree sizes. A simple multiplication factor is therefore not enough for temperature values.
The kelvin and degree Celsius have the same interval size, with t/°C = T/K − 273.15. Rankine uses Fahrenheit-sized intervals from absolute zero. The calculator rejects temperatures below absolute zero.
How to convert temperature scales
- Enter the temperature: Provide a finite value on the selected scale.
- Choose the source scale: Select °C, °F, K, or °R.
- Choose the target scale: Select the result scale or reverse the pair with Swap.
- Convert: Select Convert temperature to apply both scale and offset.
Formula and variables
The source value is converted to kelvins, validated against absolute zero, and then converted to the target scale.
K = °C + 273.15; K = (°F + 459.67) × 5/9; K = °R × 5/9- K — Kelvin value
- Thermodynamic temperature on the absolute SI scale.
- °C — Celsius value
- Kelvin value minus exactly 273.15.
- °F and °R — Fahrenheit-sized scales
- Scales using intervals of 5/9 kelvin per degree.
Convert freezing point from Celsius to Fahrenheit
Convert 0 °C to °F.
- Temperature
- 0
- From
- °C
- To
- °F
- °F = °C × 9/5 + 32
- 0 × 9/5 + 32
Result: 0 °C = 32 °F.
These are corresponding temperature values, not a ratio of the two scale readings.
Understanding your results
Values versus intervals
A change of 1 °C equals a change of 1 K, but a value of 1 °C equals 274.15 K. Use interval formulas for temperature differences.
Absolute zero
Zero kelvin equals −273.15 °C, −459.67 °F, and 0 °R. Lower values are rejected.
Assumptions
- Celsius and kelvin intervals have equal magnitude.
- The Celsius offset is exactly 273.15.
- Fahrenheit and Rankine intervals equal 5/9 kelvin.
- The input represents a temperature value rather than only an interval.
Limitations
- The calculator does not model sensor uncertainty or calibration.
- It does not convert temperature-dependent material properties.
- Interval conversion requires attention to offsets and should not reuse value equivalences blindly.
- Displayed precision cannot exceed source precision.
Common mistakes
- Multiplying Celsius by 9/5 without adding 32.
- Adding 273.15 when converting a temperature interval.
- Writing degrees Kelvin instead of kelvin.
- Accepting a value below absolute zero.
- Rounding before applying the full affine formula.
Practical use cases
Weather and cooking
Translate Celsius and Fahrenheit readings between common regional scales.
Science and engineering
Express thermodynamic temperature in kelvins or compare it with Rankine.
Planning and decision guide
Identify value or interval first
Before converting, determine whether the number is an absolute temperature reading or a temperature difference; their formulas are not identical.
Frequently asked questions
What is 0 °C in Fahrenheit?
0 °C equals 32 °F.
What is absolute zero in Celsius?
Absolute zero is exactly −273.15 °C.
Is one Celsius degree the same size as one kelvin?
Yes for intervals, but the two scales use different zero points.
Why can temperatures be negative in Celsius but not Kelvin?
Celsius places zero 273.15 kelvins above absolute zero, while kelvin starts at absolute zero.
Does this convert temperature differences?
It converts scale values. For intervals, omit the Celsius/Fahrenheit zero-point offsets and use only interval-size ratios.
Sources and review
- SI Brochure, 9th edition: thermodynamic and Celsius temperature — International Bureau of Weights and Measures. Accessed 2026-08-30.
- NIST Guide to the SI, Appendix B.9: Temperature conversion factors — National Institute of Standards and Technology. Accessed 2026-08-30.
Reviewed 2026-08-30.