Temperature Converter
Convert temperatures between Fahrenheit, Celsius and Kelvin with the exact formulas. Default: Fahrenheit to Celsius.
Last updated: October 2026
Converted Temperature
20 °C
Formula below · 2 sources (NIST, weather.gov) · Updated Oct 2026
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About this calculator
The three scales are related by exact formulas.
°F to °C: C = (F − 32) × 5/9 °C to °F: F = C × 9/5 + 32 °C to K: K = C + 273.15 °F to K: K = (F − 32) × 5/9 + 273.15
Water freezes at 32 °F (0 °C) and boils at 212 °F (100 °C) at sea-level pressure. That 180 °F span equals 100 °C, so one Celsius degree is 1.8 Fahrenheit degrees. The 32 is the offset between the two zero points. Kelvin, the SI unit, uses degrees the same size as Celsius but starts at absolute zero: 0 K = −273.15 °C = −459.67 °F. Nothing can be colder, so the calculator rejects inputs below it.
With the default, 68 °F is (68 − 32) × 5/9 = 20 °C, a comfortable room temperature.
Two handy checks: −40 is the same in both Celsius and Fahrenheit, and a normal body temperature of 98.6 °F is 37 °C.
To convert a temperature difference rather than a temperature, multiply by 9/5 or 5/9 without adding or subtracting 32: a rise of 10 °C is a rise of 18 °F.
| What | °F | °C | K |
|---|---|---|---|
| Absolute zero | −459.67 | −273.15 | 0 |
| Fahrenheit equals Celsius | −40 | −40 | 233.15 |
| Home freezer | 0 | −17.8 | 255.4 |
| Water freezes | 32 | 0 | 273.15 |
| Cool day | 50 | 10 | 283.15 |
| Room temperature | 68 | 20 | 293.15 |
| Normal body temperature | 98.6 | 37 | 310.15 |
| Hot day | 104 | 40 | 313.15 |
| Water boils (sea level) | 212 | 100 | 373.15 |
| Moderate oven | 350 | 176.7 | 449.8 |
How to use
Type the temperature, choose the unit it is in, and choose the unit you want. Example 1: 98.6 °F to Celsius. (98.6 − 32) × 5/9 = 37 °C. Example 2: 180 °C (a common oven setting) to Fahrenheit. 180 × 9/5 + 32 = 356 °F, which recipes usually round to 350 °F. Example 3: −10 °F to Celsius. (−10 − 32) × 5/9 = −23.33 °C. Watch the sign: −10 − 32 is −42, not −22. Example 4: 300 K to Fahrenheit. (300 − 273.15) × 9/5 + 32 = 80.33 °F.
Frequently asked questions
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9 (or divide by 1.8). For example, 77 °F − 32 = 45, and 45 × 5/9 = 25 °C.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (1.8), then add 32. For example, 25 °C × 1.8 = 45, and 45 + 32 = 77 °F.
Is there a quick way to estimate it in my head?
For weather temperatures, subtract 30 from Fahrenheit and halve it: 70 °F gives about 20 °C (exact: 21.1 °C). Going the other way, double the Celsius figure and add 30. The error is zero at 50 °F (10 °C) and grows to about 3 °C at 0 °F or 100 °F, so use the exact formula for cooking or medical readings.
At what temperature are Celsius and Fahrenheit equal?
At −40. Setting F = C in F = C × 9/5 + 32 gives C = −40.
Why do scientists use Kelvin?
Kelvin starts at absolute zero, so it has no negative values and ratios mean something physically. Gas laws and radiation formulas need absolute temperature. A kelvin is the same size as a degree Celsius, so you only add or subtract 273.15.
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