Convert Celsius to Fahrenheit
Celsius to Fahrenheit with the formula shown using your number, a drag-through slider, a Kelvin column and a table of reference points.
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Negative values are fine. Drag the slider for a feel of the scale.
°F = (°C × 9/5) + 32 °F = (20 × 9/5) + 32 °F = 20 × 1.8 + 32 = 68.00 °F
| degrees Celsius | degrees Fahrenheit |
|---|---|
| −40 °C | −40.00 °F |
| −20 °C | −4.00 °F |
| −10 °C | 14.00 °F |
| 0 °C | 32.00 °F |
| 4 °C | 39.20 °F |
| 10 °C | 50.00 °F |
| 16 °C | 60.80 °F |
| 20 °C | 68.00 °F |
| 25 °C | 77.00 °F |
| 30 °C | 86.00 °F |
| 35 °C | 95.00 °F |
| 37 °C | 98.60 °F |
| 38 °C | 100.40 °F |
| 40 °C | 104.00 °F |
| 60 °C | 140.00 °F |
| 100 °C | 212.00 °F |
| 180 °C | 356.00 °F |
| 200 °C | 392.00 °F |
| 220 °C | 428.00 °F |
Why you cannot just add a number
Celsius and Fahrenheit differ in two ways at once: where zero sits, and how big a degree is. Celsius puts zero at the freezing point of water and 100 at its boiling point, so there are a hundred degrees between them. Fahrenheit puts those same two points at 32 and 212, so there are a hundred and eighty. A Fahrenheit degree is therefore only 5/9 as large as a Celsius one.
That gives the formula its two parts, in this order:
°F = (°C × 9/5) + 32
Scale first, shift second. Adding 32 before multiplying is the classic error and produces an answer 25.6 degrees too high, every time.
The anchor points
| °C | °F | What it is |
|---|---|---|
| -40 | -40 | The only point where the scales agree |
| 0 | 32 | Water freezes |
| 4 | 39.2 | Fridge target temperature |
| 16 | 60.8 | Chilly indoors |
| 20 | 68 | Comfortable room temperature |
| 37 | 98.6 | Normal body temperature |
| 38 | 100.4 | Fever threshold |
| 100 | 212 | Water boils at sea level |
| 180 | 356 | A moderate oven |
Mental conversion that is actually good enough
Double it and add 30. 20 → 70 (true 68). 25 → 80 (true 77). 30 → 90 (true 86). The error grows with temperature because you are using 2 instead of 1.8, so it is within a couple of degrees for weather and hopeless for an oven. For colder values it is very good: 5 → 40 against a true 41.
The precise mental version, if you like arithmetic: subtract a tenth of the number, double it, add 32. For 20: 20 minus 2 is 18, doubled is 36, plus 32 is 68. Exact, every time.
Differences convert differently
A temperature change has no zero point to shift, so a difference converts with the 9/5 factor alone. A rise of 10 °C is a rise of 18 °F, not 50. This catches people out constantly in weather reporting and in engineering specifications, where "a 5 degree tolerance" means very different things in the two scales.
Where each scale is still used
Fahrenheit remains the everyday scale in the United States and a handful of its territories, plus informally in the Cayman Islands, Liberia and parts of the Caribbean. Everywhere else, including US scientific and medical practice, uses Celsius. The UK is genuinely bilingual: forecasts are in Celsius, but a hot summer day is still described as being "in the nineties".
Questions
What is the Celsius to Fahrenheit formula?
°F = (°C × 9/5) + 32. The multiplication comes first: the scales have different degree sizes as well as different zero points, which is why you cannot simply add 32.
At what temperature do the two scales meet?
−40. Minus forty Celsius is exactly minus forty Fahrenheit, the only point where the two scales agree.
What is 20 °C in Fahrenheit?
68 °F — mild room temperature. 25 °C is 77 °F, 30 °C is 86 °F, and 37 °C, normal body temperature, is 98.6 °F.
Is there a quick mental version?
Double it and add 30. That gives 70 for 20 °C against a true 68, and 60 for 15 °C against a true 59 — close enough for deciding on a jacket, not for an oven.