About the Temperature Converter
This temperature converter changes a reading between Celsius, Fahrenheit, Kelvin and Rankine. Type a number, choose the scale it is in, and the other three scales appear at once, with a short table of useful reference points such as freezing and boiling water. It works with negative values and rejects anything below absolute zero, the lowest temperature possible. Answers are rounded to four decimal places, which is far more precise than any household thermometer needs.
Updated October 2026
How to use the Temperature Converter
- 1Type the temperature in the number box.
- 2Choose the scale it is currently in from the Convert from list.
- 3Read the first converted value in the highlighted answer.
- 4See the other scales in the rows underneath.
- 5Press Copy result to copy all conversions.
The scales and where they are used
Celsius is used for everyday temperatures in most of the world, with water freezing at 0 and boiling at 100 at sea level. Fahrenheit is used in the United States and a few other places, with water freezing at 32 and boiling at 212. Kelvin is the SI unit for science, and Rankine is its Fahrenheit-sized cousin. Weather reports, recipes, medical readings and science all use different scales, so conversion comes up often.
Handy points to remember
- 0 °C = 32 °F, the freezing point of water
- 20 °C = 68 °F, a comfortable room
- 37 °C = 98.6 °F, normal body temperature
- 100 °C = 212 °F, boiling water at sea level
- −40 °C = −40 °F, where the scales meet
Quick mental conversion
To estimate Celsius from Fahrenheit, subtract 30 and halve it; to estimate Fahrenheit from Celsius, double it and add 30. This is only accurate within a couple of degrees near normal weather, so use the converter when precision matters, for example with ovens, lab work or fever readings.
Related tools
For other measurements use the Unit Converter and the Cooking Converter, which covers oven temperatures alongside cups and grams. The Heat Index Calculator, Wind Chill Calculator and Dew Point Calculator turn a temperature into a feels-like reading, and the Energy Converter handles heat units.
Features
- Celsius, Fahrenheit, Kelvin and Rankine
- All scales shown together
- Works with negative temperatures
- Blocks values below absolute zero
- Reference table of common temperatures
- Shows the Celsius to Fahrenheit rule
- Four decimal places
- Runs in your browser
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (1.8) and add 32. Water boils at 100 °C, so 100 × 1.8 + 32 gives 212 °F. Enter the temperature, choose Celsius and the Fahrenheit value shows immediately.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9. Normal body temperature of 98.6 °F becomes (98.6 − 32) × 5/9 = 37 °C. Choose Fahrenheit in the list to do this automatically.
At what temperature are Celsius and Fahrenheit equal?
At −40. The scales cross there because −40 × 1.8 + 32 equals −40. The reference table on this page includes it, so you can check it by typing −40 with either scale selected.
What is Kelvin used for?
Kelvin is the scientific temperature scale. It starts at absolute zero, 0 K, which equals −273.15 °C, so it has no negative values. A degree Kelvin is the same size as a Celsius degree. Physics and chemistry formulas usually need Kelvin.
What is Rankine?
Rankine is an absolute scale that uses Fahrenheit-sized degrees, starting at absolute zero (0 °R = −459.67 °F). It appears in some engineering fields in the United States, especially thermodynamics. Most people will never need it, but it is included for completeness.
What happens if I type a temperature below absolute zero?
The converter shows a message instead of a result. Nothing can be colder than absolute zero, which is −273.15 °C, −459.67 °F or 0 K, so a lower number is an input mistake rather than a real temperature.