About the Temperature Converter
The Temperature Converter shows a temperature in Fahrenheit, Celsius, Kelvin and Rankine at the same time. Type a number into any of the four boxes and the other three update as you type, so you can go from °F to °C, from °C to K or any other way without choosing a direction first.
It is handy for recipes and oven settings from other countries, weather forecasts when you travel, fever readings, science homework and lab work. Quick buttons fill in well-known temperatures such as freezing, body temperature and a 350 °F oven, and a table lists common values side by side.
The conversions use the exact formulas, shown on the page, and the tool warns you if a value is colder than absolute zero. Everything runs in your browser.
How to use it
- Type a temperatureEnter a number in the Fahrenheit, Celsius, Kelvin or Rankine box. Negative numbers and decimals work.
- Read the other scalesThe other three boxes fill in right away, and the line at the bottom sums up all four values.
- Use a quick buttonClick Absolute zero, Water freezes, Room temperature, Body temperature, Water boils or Oven for baking to fill in a known value.
- Check the formulasThe Formulas list shows how each conversion is done, so you can do it by hand or in a spreadsheet.
- Scan the quick tableThe Quick table lists twelve Celsius values from -40 to 100 with their Fahrenheit and Kelvin equivalents.
Key features
Four scales at once
Fahrenheit, Celsius, Kelvin and Rankine, all live and in sync.
Type in any box
No "from" and "to" menus. Whichever box you type in becomes the source.
Exact formulas
Uses the defining relations: °F = °C × 9/5 + 32 and K = °C + 273.15, with results to 10 significant digits.
Absolute zero check
Warns when a value is below 0 K (-273.15 °C or -459.67 °F), which is physically impossible.
Reference temperatures
Six quick buttons and a twelve-row table for the values people look up most.
Private by design
No account and no upload. The math happens in your browser.
Examples
Everyday temperatures
| °F | °C | What it is |
|---|---|---|
| 32 | 0 | Water freezes |
| 68 | 20 | Room temperature |
| 72 | 22.22222222 | A typical thermostat setting |
| 98.6 | 37 | Normal body temperature |
| 212 | 100 | Water boils at sea level |
| 350 | 176.6666667 | Oven for baking |
In Kelvin, room temperature is 293.15 K and body temperature 310.15 K.
A recipe from Europe that says 180 °C means 356 °F; most American cooks would set the oven to 350 °F, which is close enough for baking.
The formulas, step by step
To convert 98.6 °F to Celsius, subtract 32 and multiply by 5/9: (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37 °C. To go back, multiply by 9/5 and add 32: 37 × 9/5 + 32 = 66.6 + 32 = 98.6 °F.
| Conversion | Formula |
|---|---|
| °C to °F | °F = °C × 9/5 + 32 |
| °F to °C | °C = (°F − 32) × 5/9 |
| °C to K | K = °C + 273.15 |
| °F to °R | °R = °F + 459.67 |
Special points
- -40 °F is -40 °C. It is the only temperature where the two scales meet.
- 0 °F is -17.77777778 °C, and 0 °C is 32 °F.
- Absolute zero is 0 K, which is -273.15 °C, -459.67 °F and 0 °R. Type -300 in the Celsius box and you get -26.85 K with the warning "That is colder than absolute zero, which is not physically possible."
Kelvin and Rankine
Kelvin and Rankine both start at absolute zero, so they never go negative. A kelvin is the same size as a Celsius degree, and a Rankine degree the same size as a Fahrenheit degree. That is why 32 °F is 491.67 °R, and 1,000 °C is 1,273.15 K. Scientists use Kelvin; Rankine still turns up in some US engineering work.
Tips
- For a quick mental estimate from Celsius to Fahrenheit, double the number and add 30. 20 °C gives about 70 °F (the exact answer is 68 °F).
- Going the other way, subtract 30 from Fahrenheit and halve it. 80 °F is about 25 °C (exactly 26.7 °C).
- For oven temperatures, round to the nearest common setting: 180 °C is usually given as 350 °F, 200 °C as 400 °F and 220 °C as 425 °F.
- Write Kelvin without the degree sign: 300 K, not 300 °K.
- For temperature differences, such as "it warmed by 10 °C", multiply by 9/5 only: that is a rise of 18 °F, not 50 °F.
Common mistakes and limits
- Converting a temperature change with the full formulaA change of 10 °C equals a change of 18 °F. Adding 32 only applies to actual temperatures, not differences.
- Doing the steps in the wrong orderFrom Fahrenheit, subtract 32 first and then multiply by 5/9. Multiplying first gives the wrong answer.
- Using 273 instead of 273.15For most purposes the difference does not matter, but in science and engineering K = °C + 273.15 exactly.
- Expecting water to boil at 212 °F everywhereThat is at sea level. In Denver, about a mile high, water boils near 202 °F, which changes cooking times.
- Treating body temperature as a fixed line98.6 °F (37 °C) is an average. Normal readings vary from person to person and over the day. Ask a health professional about a fever.