To convert Celsius to Fahrenheit, multiply by 9/5 (or 1.8) and add 32: °F = (°C × 9/5) + 32. For the reverse, subtract 32 then multiply by 5/9: °C = (°F − 32) × 5/9. You can plug any number into our free Celsius to Fahrenheit converter and get an instant answer — but understanding the formula means you’ll never be stuck without a calculator.
The Exact Formula
The official conversion formula comes from the relationship between the two scales’ fixed reference points:
- Water freezes at 0 °C = 32 °F
- Water boils at 100 °C = 212 °F
The gap of 100 °C spans 180 °F, giving a ratio of 180/100 = 9/5 = 1.8. That’s where the multiplier comes from. The +32 accounts for the offset at the freezing point.
| Direction | Formula | Example |
|---|---|---|
| Celsius → Fahrenheit | °F = (°C × 9/5) + 32 | 20 °C → (20 × 1.8) + 32 = 68 °F |
| Fahrenheit → Celsius | °C = (°F − 32) × 5/9 | 98.6 °F → (98.6 − 32) × 0.556 = 37 °C |
Use the Fahrenheit to Celsius converter when you’re working from Fahrenheit back to Celsius.
A Fast Mental-Math Shortcut
The exact formula isn’t always practical in your head. Here’s a two-step approximation that’s accurate to within 1–2 degrees:
Celsius → Fahrenheit (quick): Double the Celsius temperature, subtract 10%, then add 32.
Example: 25 °C → 25 × 2 = 50 → 50 − 5 = 45 → 45 + 32 = 77 °F (exact: 77 °F ✓)
Fahrenheit → Celsius (quick): Subtract 32, then halve the result and add 10%.
Example: 95 °F → 95 − 32 = 63 → 63 ÷ 2 = 31.5 → 31.5 + 3.15 ≈ 35 °C (exact: 35 °C ✓)
For casual use — checking the weather, cooking, or travel — this shortcut gets you close enough without a calculator.
Common Temperature Reference Points
Memorizing a handful of landmarks makes any other temperature easy to estimate:
| Celsius | Fahrenheit | What it feels like |
|---|---|---|
| −40 °C | −40 °F | The only point where both scales are equal |
| −18 °C | 0 °F | Extremely cold winter day |
| 0 °C | 32 °F | Water freezes / ice point |
| 10 °C | 50 °F | Cool autumn day |
| 20 °C | 68 °F | Comfortable room temperature |
| 25 °C | 77 °F | Warm summer day |
| 37 °C | 98.6 °F | Normal human body temperature |
| 40 °C | 104 °F | Fever / very hot day |
| 100 °C | 212 °F | Water boils (at sea level) |
| 180 °C | 356 °F | Typical baking temperature |
When you’re traveling abroad and the weather app shows 28 °C, you know from this table it’s between 77 °F (25 °C) and 86 °F (30 °C) — a warm summer day, not a heat wave.
Where Each Scale Is Used
Celsius (°C) is the global standard. It’s used in:
- Every country except the United States, Liberia, and the Cayman Islands for everyday weather
- Scientific and medical contexts worldwide (body temperature, lab work)
- Cooking in most of the world
Fahrenheit (°F) is the dominant scale in:
- The United States for everyday weather and cooking temperatures
- Aviation in some countries (airport weather reports in the US)
- Some older engineering standards
Celsius to Fahrenheit: A Full Conversion Chart
| °C | °F | °C | °F |
|---|---|---|---|
| −30 | −22 | 25 | 77 |
| −20 | −4 | 30 | 86 |
| −10 | 14 | 35 | 95 |
| −5 | 23 | 37 | 98.6 |
| 0 | 32 | 40 | 104 |
| 5 | 41 | 50 | 122 |
| 10 | 50 | 60 | 140 |
| 15 | 59 | 75 | 167 |
| 20 | 68 | 100 | 212 |
For any temperature not in this table, use our Celsius to Fahrenheit calculator — just type the number and get the exact conversion instantly.
Why −40 Is the Same in Both Scales
The curiosity that the two scales intersect at −40 is not a coincidence — it’s built into the math. Set the two formulas equal:
°C = (°C × 9/5) + 32
°C − (°C × 9/5) = 32
°C × (1 − 9/5) = 32
°C × (−4/5) = 32
°C = −40
So at exactly −40, both thermometers read the same number. This is useful trivia, but also a useful sanity check: if you ever see a conversion claiming −40 °C ≠ −40 °F, something went wrong.
Frequently Asked Questions
What is 100 °C in Fahrenheit? 100 °C = 212 °F. This is the boiling point of water at sea level (1 atm of pressure). At higher altitudes, water boils at lower temperatures because atmospheric pressure is reduced.
What is 37 °C in Fahrenheit? 37 °C = 98.6 °F. This is the standard normal human body temperature, though healthy individuals vary between about 36.1 °C (97 °F) and 37.2 °C (99 °F) throughout the day.
What is 0 °C in Fahrenheit? 0 °C = 32 °F. This is the freezing point of water, and the offset built into the Fahrenheit formula (+32).
Is there a temperature scale that uses absolute zero? Yes — the Kelvin scale (K) starts at absolute zero (−273.15 °C / −459.67 °F). It’s used in physics and chemistry. To convert: K = °C + 273.15. There are no negative Kelvin values.
Which scale is more precise? Neither scale is inherently more precise — both can be measured to as many decimal places as your thermometer allows. The Celsius degree is slightly larger than the Fahrenheit degree (1 °C = 1.8 °F), so Fahrenheit gives finer resolution for everyday temperatures without decimals.
The Bottom Line
The Celsius-to-Fahrenheit formula is (°C × 9/5) + 32. For a quick mental estimate, double the Celsius number, subtract 10%, and add 32. Bookmark the key reference points — 0 °C = 32 °F, 20 °C = 68 °F, 37 °C = 98.6 °F, 100 °C = 212 °F — and most everyday temperature questions answer themselves.
For any exact conversion, use the free Celsius to Fahrenheit calculator or the Fahrenheit to Celsius calculator — no sign-up required.